1 Chemistry of amidyl radicals: intramolecular reactivities of alkenyl amidyl radicals YUAN L. CHOW' AND RICHARD A. PERRY' Department of Chemistry, Simon Fraser University, Burnaby, B.C., Canada V5A IS6 Received August 10, 1984 YUAN L. CHOW and RICHARD A. PERRY. Can. J. Chem. 63, 2203 (1985). Amidyl radicals possessing A4.', A'.6, and A6.' double bonds were generated from the photodecomposition of nitrosamides and chloramides and the products were identified. Dichotomies of amidyl radical reactivities were discovered and compared with published kinetic rate constants. In complete reversal to intermolecular reactivities, intramolecularly the alkenyl amidyl radicals preferentially add to the double bonds rather than abstract a C-5 hydrogen even if it is allylic. In intramolecular competition, amidyl radicals add to an acyl side chain double bond more efficiently than to an alkyl one; this is just the opposite to intramolecular H-abstraction of amidyl radicals. Taken together with the published results, it is established that, in intramolecular attacks of double bonds, amidyl radicals selectively undergo the propia-addition to generate an exo-cyclic radical rather than the longa-addition to an endo-cyclic radical: this rule should replace the old one that amidyl radicals preferentially cyclize to form five-membered rings if choices are available. YUAN L. CHOW et RICHARD A. PERRY. Can. J. Chem. 63, 2203 (1985)... On a gcntre des radicaux amidyles possedant des doubles liaisons A4.', k5.6 et A6.7 en faisant appel B la photodccornposition de nitrosamides et de chloramides et on a identific les produits obtenus. On a dccouvert les dichotomies des rcactivitcs des radicaux amidyles et on les a compare avec les constantes de vitesses cinitiques publikes anterieurement. En opposition cornplkte avec les rcactivitcs intermolcculaires, les radicaux amidyles alkcnyles s'additionnent prcfcrentiellement d'une fa~on intramolcculaire sur les doubles liaisons plut8t que d'enlever un hydrogkne en C-5, m&me s'il est allylique. Dans une compttition intramolcculaire, les radicaux amidyles s'additionnent plus facilement B une double liaison d'une chaine lattrale acyle qu'h une chaine alkyle; ce rcsultat est justement I'oppusC de ce qui se produit lors d'un enlkvement intramolcculaire de H des radicaux amidyles. Si I'on prend ces rcsultats avec ceux qui ont CtC publies anterieurement, on peut Ctablir que, lors d'attaques intramolcculaires sur des doubles liaisons, les radicaux amidyles subissent sklectivement une addition propia conduisant B un radical cyclique exo plut8t qu'une addition longa conduisant?i un radical cyclique endo: cette rkgle devrait remplacer la rkgle antcrieure selon laquelle les radicaux amidyles se cyclisent prkferentiellement pour former des cycles B cinq chainons, s'ils en ont le choix. [Traduit par le journal] Chemistry of amidyl radicals has attracted much attention in the last two decades (1-11) and been reviewed (1-4). The major interest has been the electronic configuration from which amidyl radicals (RCONR) (12-20) react with substrates and its relation to amidyl radical reactivities. Fifteen years ago, we found that N-alkylamidyl radicals interact with an olefin (e.g., 1,3-pentadiene and cyclohexene) by exclusive allylic hydrogen abstraction but no addition (21, 22);3 this preference was totally reversed in intramolecular reactivity, e.g., addition to the C(5)-atom of the olefinic bond prevailed over H-abstraction from the C(5)-allylic hydrogen (24). These observations have led us to an extensive investigation of the intramolecular reactivity of amidyl radicals (25). In the meantime, while arguments on the 2 and n amidyl radical configurations continued inconclusively, several works (14-18) on intramolecular reactivities, in particular cyclizations of alkenyl amidyl radicals, were published and interpreted in favor of 2 and (or) I I electronic configurations as the reactive state. Theoretical calculations (19, 20) on the 2-n structure of amidyl radicals have not been able to give a definitive answer (19). Recently, Ingold's group (26-29) has extended the esr observations reported earlier by Danen and Gellert (12), and proven con- vincingly that amidyl radicals (RCONR) possess n structure in their gound state; they have also determined many valuable rate constants of amidyl radical reactions by kinetic esr spectroscopy (27, 29). The availability of these finite parameters ' Author to whom correspondence may be addressed. 'present address: Merck Sharpe & Dohm, Stable Isotopes, P.O. Box 899, Point Clair - Dorval, P.Q., Canada H9R 4P7. 'A similar phenomenon was also observed, see ref. 23. allows us to discuss our old results more intelligently. We wish to publish this work now. Results The general plan was to generate amidyl radicals carrying a A4.', A5x6, or A6-' (from the N center) olefinic bond either in N-alkyl or N-acyl chains and investigate competing intramolecular H-abstraction from the C(5)-hydrogens and additions to the double bonds. It should be noted that intramolecularly, amidyl radicals preferentially abstract the C-5 hydrogens on the alkyl side chain of the N-center rather than those from the acyl side chain (9, 14), and do so from the nitrogen center but not from the amide oxygen center (14, 15). The required amides la-6a were prepared by the usual reactions and the details of their preparation have been described in the thesis submitted by one of the authors (25). Nitrosamides lb-6b were prepared by nitrosation with either NaN02 in AcOH-Ac20 or N204 in CH2C12 and the crude products were utilized in photolysis without purification since nitrosamides are generally sensitive to heat and light (9, 30). By either method, one of the side reactions was the addition of N204 or N203 to the double bond. While this addition was slower than the nitrosamide formations in general, some of these nitrosamides were contaminated with ;small amount of the addition products (see Table 1). In the preparation of 4b and 6b the contaminants amounted to as much as 15% and were clearly observable in the nmr and ir spectra. Therefore, all these nitrosamide samples were closely monitored with ir and nmr spectra before photolysis and the light source was filtered with NaNO, - sodium naphthalate filter solution to cut off the energy <400 nm in order to avoid excitation of nitro or nitrite
2 CAN. J. CHEM. VOL. 63, 1985 TABLE 1. Spectral data of N-nitrosamides and N-chloramides Nuclear magnetic resonance (ppm in CDCI3) Infrared (liquid film) Compound CH=CH CH-CONH-CH (cm- ') Ultraviolet (in benzene) nm (E) lb 5.70(m) 3.80(m) 3.10(s) 1725, (90), 408(85), 392(60), 375(50) 1 c 5.77(m) 3.10(m) 3.40(s) 1660,1440' (m) 4.40(m) 3.10(s) 1725, 1500' 422(50), 403(55), 387(40), 372(25) (m) 3.33(m) 3.08(s) 1725, (95), 404(90), 385(55), 374(40) (m)b 3.15(fd) 3.12(s) 1720, 1500' 421 (go), 402(80), 386(60), 370(20)" (1n)~ 2.79(s) 3.72(bd) 1725, 1640' 426(90), 407(85), 39 1 (50), 376(30) 6b 5.71 (m)b 2.66(s) 4.30(m) 1730, 1515' 423(6), 405(55), 390(40), 366(25) 6c 5.61(1n)~ 2.24(s) 4.55(m) "This uv spectrum was taken in CCI,. 'The integrations were less than 2H due to addition reaction. 'Weak absorptions due to the parent amides (=I640 and =I550 cm-') were observed. groups. The filter system allows us to selectively excite the n -+ T* transition band of nitrosamides and gives cleaner product formation, as demonstrated in earlier studies (30). The preparation of nitrosamides lb-6b and chloramides lc and 6c was described in the thesis (25). Their physical data are given in Table 1. Photolysis of nitrosamides under nitrogen generally gives the C-nitroso compounds as the primary photoproducts that are in equilibrium with their dimer and also tautomerize to the corresponding syn- and anti-oximes4 with a slower rate. Depending on the photolysis conditions, the C-nitroso dimer absorption in the 300-nm region can be observed and the dimers can be isolated if the photolysates are worked up quickly (9). In general, the photolysates were kept at room temperature for a long time to allow their tautomerization to oximes as shown below. The structures and stereochemistrv of svn- and anti-oximes were determined from chemical shkts and coupling patterns of could not be separated to its syn and anti isomers, but showed ir absorptions at 1670 and 1550 cm-' for a secondary amide and the chemical shifts of the olefinic protons at 6.3 and 5.8 pprn regions assignable to such conjugated oximes (33). Photolysis of lb under oxygen, other conditions being the same, was straightfonvard, giving the exo- and endo-isomeric pair of nitratolactams 9 (51%) and that of hydroxylactams 10 in addition to nitrolactams as the minor products, in agreement with the oxidative photoreaction of nitrosamides shown previously (30). The nitrolactams were obtained in only small amounts and could not be isolated. The structures of 9 and 10 were related to ketolactam 7 and arninoketone 8 by a series of hydrolysis, reduction, and oxidation as described in the Experimental. The endo- and exo-nitratolactarns 9 showed the expected ir bands at 1690, 1630, 1280, and 860 cm-' and similar ms fragmentation patterns; the endo and exo configurations were confirmed by the proton signals of CH-ONO,; the neighboring protons (e.g., N-CH,, N-CH, etc.) and the former gave a double doublet at 5.1 pprn (J = 9 and 7 Hz) characteristic ir absorptions; the correlations were well established from our previous work (31). for the axial H and the latter a narrow signal at 5.26 pprn (Wl12 = 9 Hz) for the equatorial H. Photolysis of chloramide lc was also investigated under RRCH nitrogen to give endo- and exo-chlorolactams 12 (33 and 39% \ /"O 2 RRCH-NO isolated yields), both of which showed well-defined nmr spectra and the same ms pattern; the former showed an axial proton 0 (for CHCl) at 4.25 pprn (ddd with J = 9, 7 and 1 Hz) and the 'Y latter an equatorial proton at 4.32 (dd, with J = 6 and 3 Hz). RRC=N-OH Chlorolactams 12 were easily reduced to chloroamines 14, but Photolysis of lb in benzene under nitrogen gave anti- and only endo-14 could be isolated. The exo-14 was unstable and syn-oximes 6 (2: 1 ratio, up to 68%), ketolactam 7 (18%), and reduced by LAH much more rapidly (than endo-14) to the a mixture of syn- and anti-enone oximes 11 (6%); about 4% of known amine 13 (34), due to the efficient participation of the nitratolactam 9 was also detected. The crude product contained amine in displacing the chloride; the intermediate, aziridinium the corresponding C-nitroso dimer and could be hydrolysed by ion, was obviously reduced to give the azabicyclic[3.2.1] sodium bisulfite to give ketolactam 7 in 56% yield. As syn-6 system as in 13. was slowly isomerized to anti-6 on standing, a sample of Photolysis of nitrosamide 2b under nitrogen gave syn-psyn-oxime was obtained as a mixture with anti-6. Their conlactam oxime 15 (44%) and the corresponding keto-p-lactam figurations were clearly indicated by the N-CH and N-CH, (7%); a p-lactam was indicated by the ir peak at 1725 cm-'. By protons at 3.90 and 2.82 pprn for anti-6 as compared to those decoupling experiments, the low-field doublet (C(1)-H) and at 4.65 and 2.89 pprn for syn-6. The ketolactam 7 was reduced triplet (C(6)-H) were shown to be coupled to each other with with NaBH, to endo- and exo-hydroxylactams 10, and with J = 5 Hz, in analogy to nmr data of a cis-fused lactam ring LAH followed by Jones' oxidation to aminoketone 8, the strucsystem (35). This, together with the fact that the C(1)-H is ture of which was established previously (32). Enone oxime 11 shown not to be coupled to other high-field protons, virtually eliminates the alternate structure 16 as the product. The as- 4Fiollowing the previous definition (30), the syn-oxime is the one signment of the syn orientation was based on the low chemical possessing the oximino OH on the side of the lactam ring and the shift of C(1)-H at 4.05 pprn and relatively high chemical shift anti-oxime is the one possessing that on the opposite side. of C(3)-equatorial hydrogen at 2.6 ppm in accordance with the
3 CHOW AND PERRY previous correlation (31). The keto-p-lactam was not isolated in the pure state. Successful use of BrCCl, as a radical trapping agent (32) led us to photolyze nitrosamide 3b in BrCCl, whereby single exobromolactam 17 was isolated in 89% yield. In the process, CC1,NO was also formed, as shown by the uv absorption (32) at 580 nm. The nmr spectrum became well separated on addition of Eu(fod),; decoupling experiments on this spectrum (see Experimental) clarified the coupling patterns of the protons. The coupling constants of JI,, = 8 Hz and J1,* = 1.5 HZ are in good agreement with other azabicyclo[3.3.0] derivatives (36) and confirm the exo-bromo orientation in 17. LAH reduction of 17 to the known amine 18 completed the proof of the structure (37). The preparation of nitrosamide 4b was accompanied by N204 addition to the double bond. The best sample contained a small amount of the starting amide 4a and some N204 adducts (ca. 10%); this material was used in the photolysis under nitrogen. The crude product was a complex mixture but gave anti-oxime 19 (25%) and a fraction tentatively assigned to enone oxime 21 (~7%) after extensive chromatography. The anti-oxime 19 was the only tertiary amide obtained, showing a low amide CO stretching frequency at 1605 cm-' and the OH signal at 10 ppm. The nmr triplet at 3.85 ppm indicated a more symmetrical skeleton of the [3.3.1] system than the [4.2.1] system. This chemical shift, together with the multiplet at 3.25 ppm for the equatorial C(7)- H, indicated the anti-oxime configuration. The ketolactam was reduced with LAH and oxidized by Jones' reagent to give aminoketone 22.5 All other fractions were secondary amides (ca. 1640, 1550 cm-i) that did not show typical olefinic proton signals, except for one which exhibited ir absorptions at 1635 and 1550 cm-i, and olefinic proton signals for an enone oxime (33) at the 6.2 and 6.8 ppm regions. This compound could be the oxime 21. Various difficulties prevented us from continuing the work. Photolysis of 5b under nitrogen gave syn- and anti-oximinoamides 23 (49%) and ketoamide 24 (14%). The C-nitroso dimer was also detected during irradiation (A,,, 295 nm) and tautomerized slowly to the oximes. In spite of extensive search for enone oximes, only the starting amide 5a (8%) was obtained from the crude product. The syn-oxime 23 was not isolated in the pure state but as a mixture with anti-23. This mixture was hydrolysed to ketoamide 24 as the only product. The oximes anti-23 and syn-23 exhibited the expected nmr signals(31)forthec(l)-hat4.39ppm(dd, J= 5.5 and 1 Hz) and 5.40 ppm (broad d, J = 5.9, respectively. Nitrosation of acetamide 6a was contaminated with ca. 10% of the N204 addition products as the best sample ever obtained. 'It should be mentioned that aminium radicals preferentially add to a double bond, either in intermolecular or intramolecular reactions (38).
4 CAN. J. CHEM. VOL range after photolysis. As in neither photolysis was a bicyclic acetamide detected, the work was not pursued further. Discussion Three general conclusions can be drawn from the intramolecular reactions presented here and published in the literature (17, 18). First of all, in contrast to the intermolecular reactivities reported before (21-23), intramolecular addition of amidyl radicals preferentially occurs to suitably located double bonds (e.g. A3v4, Ads5, and A5z6 from nitrogen) either in acyl or alkyl side chains to form 4, 5, and 6-membered rings, rather than to abstract C-5 hydrogens, even if these hydrogens are allylic. Secondly, the attack on these double bonds always occurs specifically in thepropia-mode (i.e. attack at the nearest end of the double bond) to generate exo-cyclic C-radicals rather than in the longa-mode (i.e. attack at the further removed end of the double bond).6 It is now established that for amidyl This sample decomposed slowly in benzene in the dark.?he new term propia-longa addition is derived from the Latin Photol~sis of this showed no formation of C-nitroso adjectives propius (near) and longus (far) to describe the pint of and the crude product gave 6a (37%) and 4-ace- attack during the course of reactions. This term is preferred over that tox~c~clohexene (9%) in addition to many minor~roducts. The of the exo-erulo cyclization (refs. 29 and 39) since conceptually the preparation and photolysis of N-chloramide 6c were even more latter can give alternative pathways and cause ambiguity in the complicated, giving at least 14 compounds in the 5-10% yield formation of polycyclic systems.
5 CHOW AND PERRY 2207 radicals propia-cyclization takes precedence over ring size considerations: e.g., A4v5, A5*6, and A6v7-alkenyl amidyl radicals cyclize to give four, five, and six-membered rings, respectively. Similar preference for propia-addition has been reported for the kinetically controlled cyclization of alkenyl C-radicals (39). Thirdly, the propia-cyclization of amidyl radicals involving the acyl chain occurs more efficiently than that involving an alkyl chain; this is in sharp contrast to the pattern of the intramolecular H-abstraction reactivity of amidyl radicals (14). These conclusions can be expanded for individual cases with reference to kinetic data reported for intramolecular reactions of amidyl radicals (27,29). As these kinetic data were obtained with open chain amidyl models, comparisons with them have to take into account semi-flexible cyclic alkenyl groups in the amidyl models used in these studies. The activation energy for intramolecular H-abstraction is 6-9 kcal/mol ranging from C-5 allylic to C-5 methyl hydrogen, and that for the propia-cyclic addition 5-8 kcal/mol in the addition to C-5 and C-6 olefinic carbons (29); it is expected that corresponding reactions in intermolecular modes will require even higher activation energies, as their rate constants of H-abstraction by arnidyl radicals suggest (-lo4 M-' s-i) (21, 29). As some cyclohexene derivatives are shown to have the activation energy of inversion (e.g. 25 $26) of 5-6 kcal/mol (40), the cyclohexene ring inversion can be faster than any inter- and intramolecular reactions. As such, the requirement for the axial orientation of the amidyl radical side chain as in 26 would not be expected to be the rate limiting factor in the intramolecular reactions. The second conclusion is best illustrated by cycloaddition of 2b, where a strained p-lactam is formed without a trace of a y-lactam, and is also shown in the N-chloramide cyclizations of 27 and 28 reported by Kuehne and Home (18). The cyclization in 28 to a four-membered ring obviously requires so high an activation energy that intermolecular reactions supersede the overall pattern; unfortunately, H-abstraction from C-5 allylic hydrogen was not carefully investigated. With two dis- tinct exceptions involving bicyclo[3.3.l]non-6-en-3-y1 amidyl radical systems, chromous chloride promoted cyclization of N-chloramides mostly follows this rule (41), indicating that chromous ions may have not changed the behavior of amidyl radicals by coordination. The first conclusion is amply substantiated by lb, lc, and 5b in this paper and other chloramides reported by others (17, 18): intramolecular addition to the C-5 olefinic carbon always occurs preferentially over H-abstraction from the C-5 allylic hydrogen. The published kinetic data on open chain amidyl radical reactions (29) show that the ratio of rate constants for the former addition to the latter H-abstraction is 22 in the competition involving acyl chains. A similar ratio for the competition involving alkyl chains is estimated7 to be 5 X 104/1 X lo7 = 11200, which is dramatically different from the nil H-abstraction observed in 5b and similar N-chloramide decompositions (17, 18). The kinetic data (29) also indicate the rate constant ratio of addition to the C-6 of a A6-7 olefinic bond to H-abstraction from a C-5 allylic hydrogen to be 1 X 106/5 X lo6 = 1/51, when involving acyl chain reactions. The observed results from the decompositions of 4b and N-chloramide 29 are just the reverse, e.g., the addition to form the sixmembered ring occurs preferentially over H-abstraction from the allylic C-5 hydrogens in acyl chain reactions (though less efficiently than A5v6 cyclization in lb and lc). There is a curious lack of H-abstraction from the C-5 allylic hydrogens located on the alkyl side of amidyl radicals generated from N-chloramide 30, even when the addition to the A6p7 double bond does not occur ( 17). The third conclusion is demonstrated by the better yields of the cyclization products from lb and lc in comparison to the poorer yield of those from 5b. This is more dramatically demonstrated in the benzoyl peroxide initiated decomposition of three series of N-chloramides (e.g. 29 vs. 30) previously'reported (17), and is also supported by kinetic data (29). It is noteworthy that amidyl radical intramolecular H-abstraction from C-5 hydrogen is far more (at least 100 times) efficient with those hydrogens in an alkyl chain than those in an acyl chain (14), just the reverse of the observed intramolecular addition reactivity. While the diverse reactivity differences described above should be intrinsically related to the 2-II radical structures of amidyl radicals, it is difficult to provide convincing explanations for all cases. As suggested by Waegel, Lessard, and co-workers (17), the C configuration of the amidyl radical could provide some rationale, albeit weak, for the observed geometry of the cyclizations. The esr results of the II-configuration with twisting of the N-CO bond open up ~1' 'COCH~ hv -F No cyclization 'The rate constant of intramolecular hydrogen abstraction by amidyl radicals from C-5 allylic -CHp-- in alkyl side chains is estimated from ref. 29 as follows. The rate ratio of abstraction from C-5 methyl hydrogens in alkyl side chains to those in acyl side chains is calculated to be 2.5. The multiplication of this ratio with the rate constant of intramolecular hydrogen abstraction from C-5 allylic (CH2) hydrogen in an acyl side chain (5 x lo6 M-' s-i) is taken as the corresponding rate constant involving an alkyl side chain.
6 2208 CAN. J. CHEM. \ wide possibilities for interpretation and they indicate that the model amides used in this and other investigations (17) are utterly powerless to correlate the reactivities with electronic configurations. Nevertheless, one suggestion can be made to rationalize the amidyl radical intramolecular reactivities, i.e., preference in addition over H-abstraction and that for acyl over alkyl side chains. It is envisaged that the amide carbonyl, being scarcely conjugated (42), may have some attractive interaction with a suitably located double bond to facilitate intramolecular addition of the nitrogen radical center. The CO group in 5 and 30 apparently has difficulties in assuming a favored conformation for such interactions; this may arise from the small barrier required for the N-CO bond twisting as proposed before (14). The observed reactivity discrepancy between esr kinetic results (28,29) and the results from product analysis (vide supra) could arise from the fact that the rate constants are determined for individual model compounds and their comparisons are intermolecular, i.e., between two different compounds. In this study, the comparisons involve intramolecular competitions in which conditions are the same for addition and abstraction reactivities. Indeed, in the kinetic studies by esr signal decays, Ingold's group (28, 29) has concluded that intramolecular reactions of amidyl radicals are very sensitive to steric factors that may still be significant over surprisingly large distances. If so, comparisons of amidyl radical reactivities even by intramolecular competitions within a molecular framework, such as in 1,4, or 5, may also be subject to subtle remote steric effects. Therefore, even if these results from product analysis are experimentally meaningful, their interpretations are beyond our present understanding. In short, the flexible and semi-flexible models utilized so far in this paper and others (17, 18), although synthetically useful, are not adequate to elucidate the details of the transition state in amidyl radical reactions and are likewise powerless to probe the electronic configurations of amidyl radicals. Experimental Unless otherwise specified, nmr spectra were recorded with a Varian A56160 spectrometer in CDC13 using TMS as the internal standard. Infrared spectra were recorded as Nujol mulls or neat liquids with a Perkin Elmer model 457 grating spectrophotometer, uv spectra with a Unicam SP800 spectrometer, and mass spectra with a Hitachi- Perkin-Elmer RMU-6E instrument at 80 ev. Melting points were recorded with a Fisher Johns hot stage apparatus and were uncorrected. Microanalyses were performed by Mr. M. K. Yang, Department of Biological Sciences, Simon Fraser University. Preparation of nitrosamides and chloramides The required amides la-6a were prepared by the usual methods and described in the thesis (25). Nitrosation of amides followed published methods (9, 32, 38) using NaNO, in AcOH-Ac20 or N204 in CH2C12. In certain cases, the addition of N204 to the alkenyl bonds also occurred to give nitrosamides contaminated by such by-products. The nitrosamides lb-66 obtained from the preparation were examined with ir and nmr spectroscopy to see the extent of the addition to double bond. These crude nitrosamide specimens were characterized by spectroscopic data (Table 1) and were used without purification. N-Chloramides were prepared by standard procedure using sodium hypochlorite (or Purfex bleach) (5, 14) and the spectroscopic data are given in Table 1. The crude products were used for photolysis without purification. Photolysis of alkenyl nitrosamides A nitrosamide (1-15 mmol) in redistilled benzene (230 ml) was irradiated with a Hanovia medium pressure Hg lamp through a NaN02 - sodium naphthalate filter solution (<400-nm cut-off) (30) while the solution was purged with dry nitrogen and cooled externally with an ice bath. At intervals, samples were taken to examine decreases of the absorption at the 405-nm region; in some cases, the intense absorption of the dimer of the C-nitroso compounds at A, 290 nm appeared. In all cases, a small sample was set in a dark place at the same temperature as the dark reaction; no decrease of the uv absorption was observed. When the 405-nm absorption disappeared (1-4 h), the photolysates were evaporated and crude products were chromatographed or treated further accordingly. 1. N-Nitroso-N-methyl-3-cylcohexene-1 -carboxamide (1 b) (a) Under nitrogen Nitrosamide lb prepared from 19 (2.2 g) in benzene (230 ml) was photolyzed to give a crude product which contained a C-nitroso dimer (ir 1220 cm-', A, 295 nm, and an nmr singlet at 2.91 ppm). On standing, the dimer disappeared. Recrystallization from EtOH-H20 gave a solid (730 mg) which was recrystallized to give anti-oxime 6, mp C; ir (KBr): 3300 (b), 3100 (m), 1670, 1230, 950, 920 cm-'; nmr (pyridine-ds): 4.09 (lh, dd, J = 5.5 and 1 Hz), (1H,m),2.74(3H,8),2.52(1H,m), (5H,m)ppm; ms (130 C), m/e (%): 168(M', 14), 152(14), 151(100), 123(14), 110(37), 98(26), 94(14), 42(40). Exact Mass calcd. for C8HI2N2O2: ; found (ms): Anal. calcd. for C8HI2N2O2: C 57.14, H 7.14, N 16.67; found: C57.27, H 7.17, N Decoupling experiments showed that neither signal at 4.08 and 2.52 ppm was coupled to the equatorial C(3)-H at 3.5 ppm. In a separate experiment, the crude residue obtained from photolysis of nitrosamide lb (amide la, 2 g, as the starting material) was heated in 50% EtOH (60 ml) with sodium bisulfite (35 g). The solution was made basic (ph 9), and was extracted with CH2C12 and chromatographed on alumina to give the first fraction, which was distilled at 84-85"C/5 Torr (1 Torr = Pa) to give ketolactam 7 (1.23 g); ir (CCL): 1735 (sh), 1715, 1645, 1400 cm-i; nmr: 3.70 (lh, dd, J = 5 and 2 Hz), 2.86 (3H, s), (7H, m) ppm; ms (30 C), m/e (%): 153(M', 64), 137(1 I), 125 (44). 110(22), 109(17), 97(100), 96(44), 80(28), 79(22), 69(67), 68(42), 42(92). Exact Mass calcd. for C8HIIN02: ; found (ms): The ketolactam 7 (1.03 g) in ether (150 ml) was refluxed with LAH (2 g, 0.05 mol) for 48 h. The ether extracts were carefully distilled with a Vigreux column to afford the corresponding volatile alcohols (32). The alcohol mixture (150 mg) was oxidized with a Jones' reagent for 20 min to give, after work-up, aminoketone 8 (90 mg); the ir, nmr, and mass spectra were identical with those of the authentic sample (32). Ketolactam 7 was reduced by NaBH4 to give a mixture of exo- and endo-hydroxylactam 10 (vide infra). A crude residue (2.4 g) from another photolysis was chromatographed on basic alumina (120 g) in the CH2C12-MeOH solvent system. Ketolactam 7 (510 mg) contaminated by a small amount of nitratolactams 9 was eluted with CH2C12. The second fraction (80 mg) was a mixture of syn- and anti-oxime 11; ir: 3400 (b), 1670 (s), 1550 (m), 1400, 1070 (m), 1050 (m); nmr: ~6.3 (lh, m), 5.75 (lh, m), (2H, m), 2.79 (3H, s); ms (30 C), m/e (%): 168(M', 67), 137(90), 109(27), 96(67), 80(87), 79(100), 55(33), 42(47). The third fraction (430 mg) was a complex mixture containing the C-nitroso dimer, 6, and 11. The fourth fraction eluted with 2-3% MeOH - CH2C12 was anti-oxime 6 (310 mg). The following fractions (810 mg) were mixtures of syn-oxime 6 (4.65 and 2.89 ppm) and anti-oxime 6 (3.90 and 2.82 ppm). A mixture of the oximes 6 (120 mg) was treated with sodium bisulfite in ethanol to afford ketolactam 7 (105 mg). (b) Under oxygen Crude nitrosamide 16 prepared from 1.2 g amide la was irradiated in benzene (230 ml) as above except that oxygen, instead of nitrogen, was bubbled through the solution. No uv absorption of the C-nitroso dimer at 295 nm was observed. The photolysate was evaporated and the crude oil chromatographed on neutral silica (65 g) eluted with 0.5% MeOH - CH2C12 to afford a mixture (970 mg) of endo- and exo-nitratolactam 9 (2: 1 ratio) contaminated with la (8%): nmr singlets at 2.95, 2.92, and 2.81 ppm. The second fraction (200 mg) was
7 CHOW AND PERRY 2209 a mixture of exo- and endo-hydroxylactams 10; ir: 3400 (b), 1670, 1070 cm-i; nmr: 4.3 (m), 3.9 (m), 2.86 (s), 2.83 (s) ppm. 'The last fraction (500 mg) was mainly 10 contaminated by nitro compounds, as shown by ir absorptions at 1680, 1550; m/e at 184; and nmr multiplet at 4.7 ppm. A portion of this fraction (90 mg) was oxidized with Jones' reagent and chromatographed to give ketolactam 7, but nitrolactam could not be isolated. The first fraction was chromatographed again to afford two nitratolactams: Exo-9; ir: 1690, 1630, 1280, 860 cm-i; nmr: 5.26 (lh, m, W = 9 Hz), 3.82 (H, m), 2.92 (3H, s), (8H, m) ppm; ms (80 C), m/e(%): 200(M', I), 168(4), 154(52), 138(19), 126(17), 110(89), 98(81), 81(22), 69(33), 55(33), 42(100). Endo-9 has the same ir pattern as exo-9; nrnr: 5.10 (IH, dd, J = 9 and 7 Hz), 3.85 (lh, bd, J = 6), 2.95 (3H, s), (8H, m) ppm; ms (75"C), m/e(%): 154(58), 138(17), 126(17), 110(100), 98(89), 83(17), 8 1(17), 69(33), 55(28), 42(100); ms(70 C), m/e(%): 200(M', l), 154(63). Hydrolysis of a mixture of exo- and endo-9 with dilute NaOH in EtOH-H20 (0.1 N) gave a mixture of exo- and endo-10 which was oxidized by Jones' reagent to ketolactam 7. A mixture of exo- and endo-9 was reduced by LAH in ether for 48 h, followed by oxidation with Jones' reagent to give aminoketone 8. N-Nitroso-N-methyl-2-cyclohexene-1 -carboxamide (2 a) The crude nitrosamide (obtained from 450 mg of 2a without purification) was photolyzed as above under nitrogen to give a residue (450 mg) which was recrystallized from benzene twice to give synoxime 15 (150 mg), mp C (dec.); ir (KBr): 3200 (b), 3080 (m), 1725 (s), 1650 (m), 1440, 935 cm-i; nmr: 8.7 (OH), 4.02 (lh, d,j=5hz),3.55(1h,t,j=5hz),2.82(3h,s), (6h,m) ppm; ms (100 C). m/e(%): 169(M' + 1, 7), 168(M', 4), 151(5), 140(5), 112(36), 111 (loo), 110(27), 94(48), 67(39), 66(63), 42(36); ms (30 C), m/e(%): 169(M' + 1, 2), 168(M', 9). Exact Mass calcd. for C8HI2N2O2: ; found (ms): Anal. calcd. for C8HI2N2O2: C 57.13, H 7.19, N 16.66; found: C 56.94, H 7.36, N The mother liquor was chromatographed on neutral alumina eluted with 0-0.5% CH30H-CH2C12 to give the first fraction (100 mg) containing 2a and the ketolactam of 15 (ir 1745 cm-i, and nmr 3.6 (m) and 1.90 (s) ppm). Elution with 5-20% MeOH - CH2C12 gave syn-oxime 15 (90 mg). Hydrolysis of 15 with sodium bisulfite gave a complex mixture. N-Nitroso-N-methyl-(2-cyclopenten-1-y1)acetamide (3b) Crude nitrosamide 36 (640 mg) in BrCCl, (230 ml) was photolyzed under nitrogen in the usual manner. The distilled solvent showed a uv absorption at 580 nm due to CC13N0. The residue was chromatographed to give 3a and exo-bromolactam 17 (730 mg) which was distilled; ir: 1685 (s), 1400 (s), 1255 (s), 600 (m); nmr: 4.2 (2H, m), 2.92 (3H, s), (6H, m), 1.5 (lh, m) ppm: gc-ms m/e(%): 219(M', 37), 217(37), 138(10), 110(100), 96(25), 82(16), 68(23), 42(29). Exact Mass calcd. for C8HI2NOBr: ; found (ms): LAH reduction of 17 gave the amine 18; the picrate from ethanol, mp C (dec.) (lit. (37) mp 207 C). Exo-bromolactam 17 (20 mg) and Eu(fod) (3 mg) in CDC13 exhibited a well-separated spectrum shown in the thesis (25). Irradiation of C(5)-H (4.6 ppm) collapsed C(1)-H (6.25 ppm) to singlet and the endo- and exo-c(4)-h (7.1 and 8.15 ppm) to an AB quartet (J = 18.5 Hz); the C(6)-H (3.15 and 3.75 ppm) coupling patterns were also changed. Irradiation of the endo-c(4)-h changed the exo-c(4)-h to a doublet (10 Hz) and C(5)-H to doublet of quartet (J = 8.9 and 3 Hz). Irradiation of exo-c(7)-h (3.0 ppm) changed endo-c(8)-h (6.05 ppm) to a double doublet (J = 3.5 and 1.5 Hz). N-Nitroso-N-methyl-(3-cyclohexen-1 -yl)acetamide(4b) A crude nitrosamide 46 contained by-products (ca. 15%) arising from the addition of N2O4 to the double bond, as shown by the nmr and ir spectra. This nitrosamide (1.39 g) in benzene was photolyzed as shown above. The crude product was chromatographed on neutral alumina to afford a mixture of unidentified secondary amides contain- ing no double bond (290 mg) as the first fraction. The second fraction eluted with 1% MeOH - CH2C12 was recrystallized from acetone to give anti-oxime 19 (250 mg), mp C (dec.); ir (CCL): 3200 (b), 3100 (b), 1605, 930 cm-i; nmr: 10.0 (OH), 3.85 (lh, t, J = 3 Hz), 3.25 (lh, m), 2.88 (3H, s), (9H, m);ms (llo C), m/e(%): 182(M', lo), 165(60), 150(40), 123(35), 110(35), 108(50), 95(10), 73(100), 58(35). Anal. calcd. for C9HI4N2O2: C 59.32, H 7.74, N 15.37; found: C 59.50, H 7.80, N The remaining fractions showed ir bands at 1640 and 1550 cm-' and only one nmr signal in the ppm region. This fraction (75 mg) was contaminated by other components and showed ir peaks at 3300 (b), 1635, 1550, 985, 970 cm-i; nmr: ~6.8 (m), 6.2 (m), 2.78 (d, on addition of D20 collapsed to singlet); ms (18O0C), m/e(%): 182(5), 165(32), 151(21), 134(21), 124(32), 106(100), 91(86), 79(36), 77(36), 73(79), 58(68), 45(36). It decomposed to a complex mixture on attempted bulb-to-bulb distillation at =10O0C. The anti-oxime 19 (80 mg) was treated with sodium bisulfite in aqueous ethanol to give ketolactam 20; ir: 1720, 1625, 1395 cm-i; ms (65"C), m/e(%): 167(M', 34), 139(20), 123(5 l), 110(100), 82(24), 73(17), 68(20), 59(37), 57(29), 42(37). Ketolactam (50 mg) was reduced in ether with LAH (150 mg) and the residue was oxidized with Jones' reagent to give the known (38) aminoketone 22 (28 mg): the picrate mp C; an identical ir spectrum with that of an authentic sample (38). N-Nitroso-N-(3-cyclohexen-1 -ylmethyl)acetamide (5b) Crude nitrosamide (1.25 g) in benzene was irradiated for 1.75 h under normal conditions to show a C-nitroso dimer uv absorption at ca. 300 nm. The crude product was chromatographed on basic alumi- na. The parent amide 5a and ketoamide 24 were eluted as mixtures with 0.5-1% MeOH - CH2C12: this was rechromatographed to give la (75 mg) and 24 (200 mg) which was distilled at 1 Torr; ir: 1725 (s), 1630 (s); nmr: 4.14 (d, J = 6 Hz), 3.65 (d, J = 3 Hz), 6.57 (bs, WIl2 = 5 Hz); ms (loo C), m/e(%): 167(M', 28), 139(25), 126(50), 110(50), 68(100), 43(56). The remaining fractions (580 mg) were mixtures of anti- and syn-oxime 23 (4: 1 ratio). The anti-oxime 23 was recrystallized from acetone, mp C (dec.); ir (KBr): 3300 (b), 1615 (s), 1460, 1420, 955, 940 cm-i; nmr: 9.5 (OH), 4.39 (lh, bd, J = 5.5 Hz), 3.51 (lh, m), 2.55 (lh, m), 2.07 (3H, s), (6H, m); ms (90 C), m/e(%): 182(M', 25), 165(8), 123(100), 85(40), 83(52), 80(17), 68(17), 59(33), 43(54). Exact Mass calcd. for C9HI4N2O2: ; found (ms): Anal. calcd. for C9HI4N2O2: C 59.32, H 7.74, N 15.37; found: C 59.18, H 7.80, N Rechromatography of the residue gave a fraction containing syn-oxime 23 as the major component (ca. 80%) and showed an nmr doublet at 5.40 (J = 5.5 Hz). A mixture of syn- and anti-oxime 23 in 6 N HCI (20 ml) was heated on a water bath for 5 h. The crude products were chromatographed to give ketoamide 24 (60 mg) and the starting oximes (25 mg). Photolysis of N-chloro-N-methyl-3-cyclohexene-1 -carboxamide (1 c) N-Chloramide lc (1.2 g) in benzene (250 ml) was photolyzed through a Vycor filter under nitrogen for 4 h. The crude product showed an nrnr singlet at 3.05 (endo-12), 2.88 (exo-12), and 2.81 (for la) in a ratio of 41 :53:6 and three gc peaks at 5.7, 5.0, and 3.5 min (for la) in a ratio of 44:49: 7. The crude product (1.4 g) was chromatographed on silicic acid (50 g) eluted with 0-3% MeOH - CH2C12 to give an oil which was distilled at 5 Torr to give exochlorolactam 12 (700 mg); ir: 1690, 1450, 815 cm-'; nmr: 4.32 (lh, dd, J = 6.0and3.0Hz), 3.70(1H, t, J = 4Hz), 2.88 (3H, s), 2.5 (lh, bm, W112 = 7 HZ), (6H, m) ppm; ms (loo C), m/e(%): 175(M', 23), 173(M', 67), 138(68), 110(100), 96(64), 83(22), 68(30), 53(29), 42(42). Exact Mass calcd. for C ~H 12~03SCI: ; found (ms): The fractions eluted with 3% MeOH - CH2C12 (700 mg) contained endo-chlorolactam 12 and la and were rechromatographed to give endo-12; ir: 1690, 1450, 765, 750 cm-'; nmr: 4.25 (1 H, ddd, J = 9, 7, and 1 Hz), 3.86 (lh, dd, J = 5.5 and 1 Hz), 3.05 (3H, s), (7H, m) ppm; ms showed the same pattern as that of exo-12. An ether solution of exo-12 (100 mg) and LAH (0.8 g) in ether was
8 2210 CAN. J. CHEM. VOL. 63, 1985 set aside for 5 days. The crude oil obtained was treated with picric acid in benzene; the precipitate was recrystallized from EtOH to afford the picrate of bicyclic amine 13, mp 255 C (dec.) (lit. (34) mp 250 C). Anal. calcd. for CI4Hl8N4O7: C 47.46, H 5.08, N 15.82; found: C 47.69, H 5.12, N A crude product (1.2 g) containing exo-12, endo-12, and la in a ratio of 48:42: 10 in ether was stirred with LAH (3 g) and aliquots were removed at intervals for work-up and examined with gc. In 10 h, the above three peaks disappeared and were replaced by peaks at 1.7 (13), 1.8 (methyl-3-cyclohexenylmethylamine), and 3.5 (endochloramine 14) min. After this, the peak of 13 gradually increased at the expense of the peak of endo-14. In 30 h, the latter disappeared to give only the former peak. LAH reduction of a crude product was stopped at 10 h, and the reaction was worked up to give a crude product that was chromatographed to give endo-chloramine 14 (360 mg); ir: 1450,780 cm-i; nmr: 3.2 (h, ddd, J = 9,7 and 1.5 Hz), 2.96 (2H,m),2.52(3H,s),2.45(1H,b, W,,,= 5), (7H,m)ppm; ms (10O0C), m/e(%): 161(M+, 12), 159(M+, 32), 124(22), 96(32), 82(100), 67(16), 55(18), 42(50). The ir and nmr spectra were superimposable with an authentic sample (42). Further elution afforded amine 12 and N-(3-cyc1ohexenyl)methylmethylamine. When exo-chlorolactam 12 (180 mg) was reduced with LAH (1 g) for 5 h in ether, it gave 13 and what appeared to be the exo-chloramine 14 as a 1:3 mixture; ir: 1450, 760 cm-i; nmr: 4.3 (2H, m), 2.8 (lh, m), 2.43 (3H, s), pprn (8H, m) ppm. This compound decomposed on standing at room temperature. Acknowledgement The authors are grateful to the Natural Sciences and Engineering Research Council of Canada, Ottawa, for generous financial aid for this project. 1. R. S. 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