The Mannich reaction in the synthesis of N,S-containing heterocycles 10*. Recyclization of stable cyclic Michael adducts,

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1 Russian Chemical Bulletin, International Edition, Vol. 58, No. 7, pp , July, The Mannich reaction in the synthesis of N,S-containing heterocycles 10*. Recyclization of stable cyclic Michael adducts, N-methylmorpholinium 6-R-6-hydroxy-1,4,5,6-tetrahydropyridine-2-thiolates, to pyrimido[4,3-b][1,3,5]thiadiazines under conditions of aminomethylation reaction V. V. Dotsenko, a,b K. A. Frolov, a S. G. Krivokolysko, a and V. P. Litvinov c a V. Dal East-Ukrainian National University, ChemEx Laboratory, 20a Molodezhnyi kv., Lugansk, Ukraine. Victor_Dotsenko@bigmir.net b State Enterprise Luganskstandardmetrology, 50 ul. Timiryazeva, Lugansk, Ukraine c N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., Moscow, Russian Federation 5-Substituted N-methylmorpholinium 4-aryl-6-R-3-cyano-6-hydroxy-1,4,5,6-tetrahydropyridine-2-thiolates upon the action of primary amines and HCHO in ethanol undergo recyclization to 3,7-disubstituted 8-aryl-3,4,7,8-tetrahydro-2H,6H-pyrimido[4,3-b][1,3,5]thiadiazine-9-carbonitriles in low yields (5 28%). The latter were also obtained by alternative method, viz., by sequential condensation of cyanothioacetamide with aromatic aldehydes, primary amines, and HCHO. Key words: the Mannich reaction, pyridine-2-thiolates, aminomethylation, pyrimido[4,3-b]- [1,3,5]thiadiazines, recyclization, the retro Michael reaction. The literature data 2 8 show that 2-mercaptopyridines, tautomeric to them pyridine-2(1h)-thiones, or the corresponding thiolates extremely ready undergo the Mannich reaction, however, in most cases it is a nontrivial problem to predict the product structures and direction of the aminomethylation reaction. Decisive factors influencing regioselectivity of the process are the medium рh and especially the structure of mercaptopyridine substrate. For instance, the following compounds were described as aminomethylation products: 2-(aminomethyl)thiopyridines, 2 pyrido[2,1-b][1,3,5]thiadiazines, 3 pyrido[1,2-a][1,3,5]- triazines, 4 3,7-diazabicyclo[3.3.1]nonane, 5 3,5,7,11-tetraazatricyclo[ ,7 ]tridec-2-enes, 6 8-thioxospiro- [3,5,7,11-tetraazatricyclo[ ,7 ]tridec-2-en-13,4 piperidine]-1,9-dicarbonitriles, 7 bis(pyrido[2,1-b][1,3,5]- thiadiazin-7-yl)methanes. 8 In continuation of our research in the field of aminomethylation of functionally substituted pyridine-2-thiolates, we decided to study behavior of piperidinium (4R*,5R*,6R*)-5-benzoyl-4-(2-chlorophenyl)-3-cyano-6-hydroxy-6-methyl-1,4,5,6-tetrahydropyridine-2-thiolate (1) under conditions of the "double" Mannich condensation. * For Part 9, see Ref. 1. Deceased. Thiolate 1 is easily synthesized by polycomponent condensation of cyanothioacetamide, 2-chlorobenzaldehyde, benzoylacetone, and piperidine; the reaction is regiospecific. 9 Being a stable Michael adduct, thiolate 1 is potentially capable of both further dehydration and transformation to 1,4-dihydropyridine derivative and the retro Michael reaction with the liberation of benzoylacetone and (E)-3-aryl-2-cyanoprop-2-enethioamide (2). In fact, this is the latter version which is implemented under aminomethylation conditions. Treatment of thiolate 1 with 2 equiv. of p-toluidine and excess formaldehyde leads to pyrimido[4,3-b][1,3,5]thiadiazine (5a) as the only isolable reaction product instead of expected bispydine derivatives 3 or pyrido[2,1-b][1,3,5]thiadiazine (4) (Scheme 1). In favor of the intermediate formation of thioamide 2 testifies the fact that compound 5 and its analogs can be easily synthesized by aminomethylation of unsaturated thioamides 2 (see Ref. 10), as well as by polycomponent reaction of aromatic aldehydes, cyanothioacetamide, primary amines, and formaline in weakly basic medium and by recyclization of 2,6-diamino-3,5-dicyano-4H-thiopyrans in the presence of RNH 2 /HCHO. 11 To sum up, the aminomethylation of thiolate 1 initially gives thioamides 2 through the retro Michael reaction, which are further aminomethylated to pyrimido[4,3-b][1,3,5]thiadiazines 5. When ben- Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp , July, /09/ Springer Science+Business Media, Inc.

2 1480 Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009 Dotsenko et al. zylamine is involved into the reaction instead of p-toluidine, a tar-like product of complex composition was obtained, in which pyrimidothiadiazine (5b) and perhydro-1,3,5-triazine (6) were identified by TLC (see Scheme 1). It should be noted that this reaction has a general character: for instance, other cyclic Michael adducts, such as N-methylmorpholinium 4-aryl-3-cyano-5-ethoxycarbonyl-6-hydroxy-6-phenyl-1,4,5,6-tetrahydropyridine-2-thiolates (7a,b) (see Ref. 12) and N-methylmorpholinium 5-benzoyl-4-(2-chlorophenyl)-3-cyano-6-hydroxy-6-phenyl-1,4,5,6-tetrahydropyridine-2-thiolate (8) (see Ref. 13), under the Mannich reaction conditions undergo similar recyclization with elimination of 1,3-dicarbonyl component and formation of the same pyrimido[4,3-b]- [1,3,5]thiadiazines 5 (Scheme 2). The yields in this reaction are rather low and do not exceed 28%; no additional amount of the product was obtained from the mother solution. Using transformation of thiolate 7b to compound 5d as an example, it was shown that the ratio substrate : primary amine of 1 : 4 (with constant excess of Table 1. Dependence of the yields of compound 5d on the reaction conditions and the ratio substrate : amine in the recyclization reaction of thiolate 7b Com p-toluidine Conditions Yield of 5d pound /mmol equiv. (%) НСНО Т/ C 7b/mmol /mmol / * / * / * / /4 34 ** / * 16.4 * Heating to 20 C. ** Reflux for 3 h. formaline) was the optimum from the point of the recyclization product yield (Table 1). It seems quite probable that some primary amine and HCHO are consumed in aminomethylation of 1,3-dicar- Scheme 1 B = ; R = 4-MeC 6 H 4 (5a), R = CH 2 Ph (5b); Ar = 2-ClC 6 H 4

3 Pyrimido[4,3-b][1,3,5]thiadiazines Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, B = ; Scheme 2 Com- Ar R pound 5a 2-ClC 6 H 4 4-МеC 6 H 4 5c Ph Ph 5d 4-ClC 6 H 4 4-МеC 6 H 4 7a Ph 7b 4-ClC 6 H 4 bonyl compounds, dibenzoylmethane and ethyl benzoylacetate, eliminating in the reaction course. For the recyclization to be a success, it is optimum to perform the reaction under mild conditions (a short-time heating to 20 C), since both a prolonged reflux of the mixture of thiolate 7b, p-toluidine, and HCHO in EtOH and keeping the starting reactants in EtOH at 20 C lead to resinification of the reaction mixture. Finally, it is also necessary to note that for the analogs of cyclic adducts 1, 7, and 8, there are described only separate examples of transformations leading to recyclization/destruction of the tetrahydropyridine ring. For instance, in a number of cases there was found abnormal recyclization of 6-alkyl-3-cyano-6-hydroxy-1,4,5,6-tetrahydropyridine-2-thiolates to (E)-3-aryl-2-(thiazol-2- yl)acrylonitriles during attempted alkylation with α-haloketones. 14,15 Pyrimido[4,3-b][1,3,5]thiadiazines 5 are colorless or pale yellow finely crystalline substances virtually insoluble in EtOH, moderately soluble in acetone, and readily soluble in warm DMF or DMSO. The recyclization products 5a,d were characterized by spectroscopic methods and proved identical to the samples obtained by aminomethylation 10 of unsaturated thioamides 2. The structures of compounds 5c,d were confirmed by alternative synthesis from corresponding aromatic aldehyde, cyanothioacetamide (9), primary aromatic amine, and formaldehyde with the yields of pyrimido[4,3-b][1,3,5]thiadiazines being 19 and 58%, respectively. It should be especially noted that the synthesis of 3,7,8-triphenyl-3,4,7,8-tetrahydro- 2H,6H-pyrimido[4,3-b][1,3,5]thiadiazine-9-carbonitrile (5c) by aminomethylation of the corresponding 2-cyanothioacetamide according to the method described in the literature 10 is hindered due to the difficulties in the preparation of the latter and its tendency to dimerization by the type of [4+2]-cycloaddition. 16 The IR spectra of pyrimidothiadiazines 5 exhibit intensive absorption bands related to the stretching vibrations of the conjugated cyano group (ν = cm 1 ). In the 1 H NMR spectra of compounds 5, in addition to characteristic signals for the aromatic substituents there are present a singlet for the protons C(8)H at δ , a set of the signals for three methylene groups, two pairs of doublets N CH 2 N in the region δ , two doublets for the protons N CH 2 S shifted toward the up-field region (δ ). In conclusion, N-methylmorpholinium 4-aryl-5-cyano-6-hydroxy-1,4,5,6-tetrahydropyridine-2-thiolates upon the action of a primary amine and formaline undergo recyclization to form 3,7-disubstituted 8-aryl-3,4,7,8- tetrahydro-2h,6h-pyrimido[4,3-b][1,3,5]thiadiazine-9- carbonitriles. The method cannot be used for preparative purposes due to the low yields and availability of more convenient and efficient methods for obtaining the target pyrimido[4,3-b][1,3,5]thiadiazines. In particular, such a method consists in the sequential one-pot condensation of an aldehyde, cyanothioacetamide, a primary amine, and formaline. Experimental 1 H NMR spectra were recorded on a Bruker Avance II 400 spectrometer ( MHz) (for compound 1, Bruker AM-300 (300 MHz)) in DMSO-d 6 with Me 4 Si as an internal standard. IR spectra were recorded on a IKS-29 spectrophotometer in Nujol. Elemental analysis was performed on a Perkin-Elmer C,H,N-Analyzer. The individuality of compounds synthesized was monotored by TLC on Silufol UV 254 plates in acetone n-heptane (1 : 1) solvent system, visualization was performed by iodine vapors or UV detector. Melting points were measured on a Kofler stage and uncorrected. The starting N-methylmorpholinium 4-aryl-3-cyano-5-ethoxycarbonyl-6-hydroxy-6-phenyl-1,4,5,6- tetrahydropyridine-2-thiolates 7a,b and N-methylmorpholinium 5-benzoyl-4-(2-chlorophenyl)-3-cyano-6-hydroxy-6-phenyl-1,4,5,6-tetrahydropyridine-2-thiolate (8) were obtained according to the known procedures. 12,13 Perhydro-1,3,5-triazine 6 for comparative analysis was obtained by condensation of formaline with benzylamine. 17

4 1482 Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, 2009 Dotsenko et al. Piperidinium (4R*,5R*,6R*)-5-benzoyl-4-(2-chlorophenyl)- 3-cyano-6-hydroxy-6-methyl-1,4,5,6-tetrahydropyridine-2-thiolate (1) was obtained according to the procedure given in the Dr. Sci. Thesis: 9 cyanothioacetamide (2.0 g, 20 mmol), benzoylacetone (3.25 g, 20 mmol) (after 5 min), and piperidine (2.5 ml, 25 mmol) were sequentially added to a mixture of 2-chlorobenzaldehyde (2.3 ml, 20 mmol) and piperidine (3 drops) in EtOH (30 ml) (temperature, 20 C) with stirring. After 3 h, a precipitate formed was filtered off and washed with acetone to obtain thiolate 1 (7.7 g, 82%) as a white finely crystalline powder, m.p C. Found (%): C, 63.66; H, 5.94; N, C 25 H 28 ClN 3 O 2 S (M = ). Calculated (%): C, 63.88; H, 6.00; N, IR (Nujol), ν/cm 1 : 3450, 3214 (OH, NH, NH 2 + ), 2173 (CN), 1697 (C=O). 1 H NMR (DMSO-d 6 ), δ: 1.58 (m, 6 H, (CH 2 ) 3 ); 1.75 (s, 3 H, CH 3 ); 3.01 (m, 4 H, CH 2 NCH 2 ); 4.13 and 4.27 (both d, 1 H each, C(4)H and C(5)H, 3 J = 11.8 Hz); 6.08 (m, 10 H, Ph, 2-ClC 6 H 4, OH); 8.32 (br.s, 1 H, NH). The relative configuration (4R*,5R*,6R*) was assigned to thiolate 1 based on the X-ray diffraction data for the S-alkylation product. 9 Reaction of piperidinium (4R*,5R*,6R*)-5-benzoyl-4-(2- chlorophenyl)-3-cyano-6-hydroxy-6-methyl-1,4,5,6-tetrahydropyridine-2-thiolate (1) with primary amines and HCHO. Excess of 37% aqueous HCHO (3 ml, 40 mmol) (free of paraformaldehyde) and p-toluidine (0.3 g, 2.8 mmol) (or benzylamine (0.3 ml, 2.8 mmol)) were added to a suspension of pyridine-2-thiolate 1 (0.6 g, 1.28 mmol) in EtOH (15 ml), the mixture obtained was heated until it was homogenized, filtered through a folded filter, and kept at 20 C. In the case of p-toluidine, already after 15 min a pale yellow precipitate of pyrimido[4,3-b][1,3,5]thiadiazine 5a was formed, which after 48 h was filtered off and washed with EtOH. In the case of benzylamine, an oil obtained crystallized to a yellow tar-like substance on prolonged (1 month) standing, which was (TLC, NMR) a complex multicomponent mixture. According to the comparative TLC data, in addition to unidentified products, the mixture contained pyrimido[4,3-b][1,3,5]- thiadiazine 10 5b (R f 0.60) and 1,3,5-tribenzylperhydro-1,3,5-triazine 17 6 (R f 0.73). We failed in our attempts to separate this mixture by recrystallization or chromatography. Reaction of N-methylmorpholinium 4-aryl-3-cyano-5-eth- oxycarbonyl-6-hydroxy-6-phenyl-1,4,5,6-tetrahydropyridine-2- thiolates (7a,b) with primary amines and HCHO. Excess of 37% aq. HCHO (2 ml, 27 mmol) (free of paraformaldehyde) and corresponding primary amine (4 equiv., mmol) were added to a suspension of pyridine-2-thiolate 7a,b ( mmol) in EtOH (15 ml), the mixture obtained was refluxed for 1 2 min until the starting reactants were completely dissolved, filtered through a folded filter, and kept for 4 5 days at 20 C. The solvent was decanted, a tar-like product was treated with boiling EtOH (8 10 ml). An insoluble precipitate of the corresponding pyrimido[4,3-b][1,3,5]thiadiazine 5c,d was filtered off, washed with EtOH, and recrystallized from suitable solvent. The reactions of thiolate 7b with HCHO and p-toluidine (1 equiv., 2 equiv., and 6 equiv.) were performed similarly. The results are given in Table 1. Reflux (3 h) of a mixture of thiolate 7b, p-toluidine (4 equiv.) and excess HCHO in ethanol led to resinification of the reaction mixture, from which we failed to isolate compound 5d. Reaction of N-methylmorpholinium 5-benzoyl-4-(2-chlorophenyl)-3-cyano-6-hydroxy-6-phenyl-1,4,5,6-tetrahydropyridine-2-thiolate (8) with formaline and p-toluidine. A mixture of thiolate 8 (1.0 g, 1.8 mmol), p-toluidine (0.39 g, 3.65 mmol), and 37% aq. HCHO (2.5 ml, 34 mmol) (free of paraformaldehyde) in EtOH (20 ml) was brought to boiling, the solution formed was filtered through a paper filter. The mixture was kept for 4 days at 20 C, a precipitate was filtered off and washed with hot EtOH to obtain pyrimido[4,3-b][1,3,5]thiadiazine 5a (0.24 g, 28%). Analytically pure sample was obtained by recrystallization from acetone EtOH (1 : 1) solvent mixture. Synthesis of pyrimido[4,3-b][1,3,5]thiadiazines (5c,d) by sequential condensation of aldehyde, cyanothioacetamide, primary amine, and formaldehyde. A mixture of cyanothioacetamide 9 (0.3 g, 3 mmol), N-methylmorpholine (2 drops), and p-chlorobenzaldehyde (0.42 g) (or freshly distilled PhCHO (0.31 ml, 3 mmol)) in EtOH (15 ml) was stirred for 30 min, after that 37% aq. formaline (2 ml, 27 mmol) (free of paraformaldehyde) and primary amine (6.6 mmol) (freshly distilled aniline (0.6 ml) for 5c or p-toluidine (0.71 g) for 5d) were added to the reaction mixture. The mixture obtained was refluxed for 3 5 min with intensive stirring, kept for 48 h at 20 C, the solvent was decanted, and a tar-like residue was treated with boiling ethanol. The product was filtered off, washed with water and hot EtOH and recrystallized from suitable solvent to obtain analytically pure pyrimido[4,3-b][1,3,5]thiadiazines 5c,d. 8-(2-Chlorophenyl)-3,7-di(4-methylphenyl)-3,4,7,8-tetrahydro-2H,6H-pyrimido[4,3-b][1,3,5]thiadiazine-9-carbonitrile (5a). A pale yellow finely crystalline powder, the yield was 5% on thiolate 1, 28% on thiolate 8. M.p C (decomp., from acetone : EtOH = 1 : 1) (cf. Ref. 10: C (DMF)). Found (%): C, 67.95; H, 5.30; N, C 27 H 25 ClN 4 S (M = = ). Calculated (%): C, 68.56; H, 5.33; N, IR (Nujol), ν/cm 1 : 2165 (C N). 1 H NMR (DMSO-d 6 ), δ: 2.26 and 2.30 (both s, 3 H each, 2 MeC 6 H 4 ); 4.07 and 4.57 (both d, 1 H each, SCH 2 N, 2 J = 13.0 Hz); 4.70 and 4.86 (both d, 1 H each, NCH 2 N, 2 J = 13.2 Hz); 5.06 and 5.26 (both d, 1 H each, NCH 2 N, 2 J = 12.4 Hz); 5.24 (s, 1 H, C(8)H); 6.78 and 6.91 (both d, 2 H each, 4-MeC 6 H 4, 3 J = 8.5 Hz); 7.00 and 7.05 (both d, 2 H each, 4-MeC 6 H 4, 3 J = 8.6 Hz); (m, 4 H, 2-ClC 6 H 4 ). 3,7,8-Triphenyl-3,4,7,8-tetrahydro-2H,6H-pyrimido[4,3-b]- [1,3,5]thiadiazine-9-carbonitrile (5c). A beige finely crystalline powder, the yield was 12% on thiolate 7a, in the condensation reaction of thioamide 9 with PhCHO, PhNH 2, and HCHO, the yield was 19%. M.p C (acetone EtOH = 2 : 1). Found (%): C, 72.49; H, 5.34; N, C 25 H 22 N 4 S (M = ). Calculated (%): C, 73.14; H, 5.40; N, IR (Nujol), ν/cm 1 : 2161 (C N). 1 H NMR (DMSO-d 6 ), δ: 4.17 and 4.67 (both d, 1 H each, SCH 2 N, 2 J = 13.1 Hz); 4.86 and 4.96 (both d, 1 H each, NCH 2 N, 2 J = 12.9 Hz); 5.10 and 5.29 (both d, 1 H each, NCH 2 N, 2 J = 12.5 Hz); 5.18 (s, 1 H, C(8)H); (m, 15 H, 3 Ph). 8-(4-Chlorophenyl)-3,7-di(4-methylphenyl)-3,4,7,8-tetrahydro-2H,6H-pyrimido[4,3-b][1,3,5]thiadiazine-9-carbonitrile (5d). A snow-white finely crystalline powder, the yield was 17.5% on thiolate 1 and 58% on thioamide 9, 4-ClC 6 H 4 CHO, 4-MeC 6 H 4 NH 2, and HCHO. M.p C (decomp., from a DMF EtOH = 1 : 1 solvent mixture; cf. Ref. 10: C (EtOH)). Found (%): C, 68.05; H, 5.31; N, C 27 H 25 ClN 4 S (M = ). Calculated (%): C, 68.56; H, 5.33; N, IR (Nujol), ν/cm 1 : 2175 (C N). 1 H NMR (DMSO-d 6 ), δ: 2.23 and 2.24 (both s, 3 H each, 2 MeC 6 H 4 ); 4.02 and 4.61 (both d, 1 H each, SCH 2 N, 2 J = 13.0 Hz); 4.83 and 4.92 (both d, 1 H each, NCH 2 N, 2 J = 13.2 Hz); 5.17 (s, 1 H, C(8)H); 5.10 and

5 Pyrimido[4,3-b][1,3,5]thiadiazines Russ.Chem.Bull., Int.Ed., Vol. 58, No. 7, July, (both d, 1 H each, NCH 2 N, 2 J = 12.2 Hz); (m, 8 H, two groups of signals for p-tolyl substituents 4-H 3 CC 6 H 4 are overlapped); 7.32 and 7.42 (both d, 2 H each, 4-ClC 6 H 4, 3 J = 8.5 Hz). References 1. V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Izv. Akad. Nauk, Ser. Khim., 2009, 1479 [Russ. Chem. Bull., Int. Ed., 2009, 58, 1524]. 2 I. M. Orudzheva, T. E. Efendiev, S. M. Aliev, Zh. Org. Khim., 1981, 17, 410 [Russ. J. Org. Chem. (Engl. Transl.), 1981, 17]. 3. (a) V. V. Dotsenko, S. G. Krivokolysko, whereas. N. Chernega, V. P. Litvinov, Dokl. Akad. Nauk, 2003, 389, 763 [Dokl. Chem. (Engl. Transl.), 2003, 389, 92]; (b) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Monatsh. Chem., 2008, 139, V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Khim. Geterotsikl. Soedin., 2007, 621 [Chem. Heterocycl. Compd. (Engl. Transl.), 2007, 43, 517]. 5. (a) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov. Khim. Geterotsikl. Soedin., 2005, 1695 [Chem. Heterocycl. Compd. (Engl. Transl.), 2005, 41, 1428]; (b) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Monatsh. Chem., 2007, 138, 489; (c) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Izv. Akad. Nauk, Ser. Khim., 2007, 2397 [Russ. Chem. Bull., Int. Ed., 2007, 56, 2482]. 6. (a) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Izv. Akad. Nauk, Ser. Khim., 2005, 2605 [Russ. Chem. Bull., Int. Ed., 2005, 54, 2692]; (b) V. V. Dotsenko, S. G. Krivokolysko, A. N. Chernega, V. P. Litvinov, Monatsh. Chem., 2007, 138, 35; (c) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Izv. Akad. Nauk, Ser. Khim., 2007, 1014 [Russ. Chem. Bull., Int. Ed., 2007, 56, 1053]. 7. (a) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Khim. Geterotsikl. Soedin., 2007, 1709 [Chem. Heterocycl. Compd. (Engl. Transl.), 2007, 43, 1455]; (b) V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, E. B. Rusanov, Dokl. Akad. Nauk, 2007, 413, 345 [Dokl. Chem. (Engl. Transl.) 2007, 413, 68]. 8. V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Monatsh. Chem., 2008, 139, S. G. Krivokolysko, Dr. Sci. Thesis, MSU, Moscow, 2001 (in Russian). 10. V. V. Dotsenko, K. A. Frolov, S. G. Krivokolysko, A. N. Chernega, V. P. Litvinov, Monatsh. Chem., 2006, 137, V. V. Dotsenko, S. G. Krivokolysko, V. P. Litvinov, Izv. Akad. Nauk, Ser. Khim., 2007, 1420 [Russ. Chem. Bull., Int. Ed., 2007, 56, 1474]. 12. A. A. Krauze, E. E. Liepin sh, Yu. E. Pelcher, Z. A. Kalme, G. Ya. Dubur, Khim. Geterotsikl. Soedin., 1987, 75 [Chem. Heterocycl. Compd. (Engl. Transl.), 1987, 61]. 13. S. G. Krivokolysko, V. D. Dyachenko, A. N. Chernega, V. P. Litvinov, Khim. Geterotsikl. Soedin., 2001, 790 [Chem. Heterocycl. Compd. (Engl. Transl.), 2001, 37, 727]. 14. S. G. Krivokolysko, V. D. Dyachenko, V. N. Nesterov, V. P. Litvinov, Khim. Geterotsikl. Soedin., 2001, 929 [Chem. Heterocycl. Compd. (Engl. Transl.), 2001, 37, 855]. 15. S. G. Krivokolysko, V. D. Dyachenko, V. P. Litvinov, Khim. Geterotsikl. Soedin., 1999, 1370 [Chem. Heterocycl. Compd. (Engl. Transl.), 1999, 35, 1190]. 16. J. S. A. Brunskill, A. De, D. F. Ewing, J. Chem. Soc., Perkin Trans. 1, 1978, J. Graymore, J. Chem. Soc., 1932, Received February 4, 2009