BOC-Protected Amines via a Mild and Efficient One-Pot Curtius Rearrangement. Hélène Lebel* Olivier Leogane. Supporting Information

Transcription

1 BC-Protected Amines via a Mild and Efficient ne-pot Curtius Rearrangement. élène Lebel* livier Leogane Département de chimie, Université de Montréal, Montréal, Québec, Canada, 3C 3J7 Supporting Information General information S2 Curtius procedure S3 Characterization of carbamate products... S3 S1

2 General: Unless otherwise noted, all non-aqueous reactions were performed under an oxygen-free atmosphere of argon with rigid exclusion of moisture from reagents and glassware. The solvents were dried using standard methods prior to use. Zn(Tf) 2, NaN 3 and Bu 4 NBr are commercially available and were purchased from Aldrich. (1 R,3R)-2-(3 -(2-xopropyl)-acetyl-2,2 - dimethylcyclopropyl)acetic acid was prepared from (-)-3-carene according to the litterature. 1 (2R)- Methyl-3-tert-butyldiphenylsilanyloxypropionic acid (10) was prepared from (R)-(-)-3-hydroxy-2- methylpropionic methyl ester according to the litterature. 2 Dialkyl malonates, prepared by double alkylation of diethylmalonate, were partially hydrolyzed to lead to -ester carboxylic acid according to the litterature. 3 ther carboxylic acids are commercially available and were purified using standard methods prior to use. Analytical thin layer chromatography (TLC) was performed using EM Reagent 0.25 mm silica gel 60-F plates. Visualization of the developed chromatogram was performed by UV absorbance, aqueous cerium molybdate, ethanolic phosphomolybdic acid, or aqueous potassium permanganate. Flash chromatography was performed using EM Silica Gel 60 ( mesh) with the indicated solvent system. ptical rotations were measured on a Perkin- Elmer 341 digital polarimeter at 589 nm. Data are reported as follows: [ ] l temp., concentration (c g/100ml), and solvent. 1 NMR spectra were recorded in CDCl 3, unless otherwise noted, on a Bruker AV-400, a Bruker ARX-400, a Bruker AMX-300 or a Bruker AV-300 spectrometers (400, 400, 300 and 300 Mz respectively). Chemical shifts are reported in ppm on the scale from an internal standard of residual chloroform (7.27 ppm). Data are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, qn = quintet, m = multiplet and br = broad), coupling constant in z, integration. 13 C NMR spectra were recorded in CDCl 3, unless otherwise noted, on a Bruker AV-400, a Bruker ARX-400, a Bruker AMX-300 or a Bruker AV-300 spectrometers (100, 100, 75 and 75 Mz respectively) with complete proton decoupling. Chemical shifts are reported in ppm from the central peak of CDCl 3 (77.0 ppm) on the scale. Peak assignment was confirmed with 2D CSY experiments. Mass spectra were obtained on a LC-MSD TF (ESI) Agilent Technologies high resolution from the Centre régional de spectrométrie de masse de l Université de Montréal. Analytical Supercritical Fluid Chromatography (SFC) was performed on a Berger SFC Analytical Instrument equipped with diode-array UV detector. Values for enantiomeric excess were determined using a chiral column. Data are reported as follows: column type, flow, solvent used, and retention time (t r ). Analytical gas chromatography with a mass spectroscopy (GC-MS) was carried out on a ewlett Packard 6890 series gas chromatograph equipped with a split mode capillary injector and electron impact mass detector. Unless otherwise noted, injector and detector temperatures were 250 C and the carrier gas was hydrogen (2 ml/min) with a P-5MS column. Data are reported as follows: column type, oven temperature, and retention time (t r ). 1 a) Moglioni, A. G.; Garcìa-Expòsito, E. G. ; Aguado, G. ; Parella, T. ; Branchadell, V. ; Moltrasio, G. Y. ; rtuno, R. M. J. rg. Chem. 2000, 5, b) Fernàndez, F.; Lòpez, C.; ergueta, A.R. Tetrahedron 1995, 51, c) Librando, V.; Tomaselli, G. ; Tringalli, G. Ann. Chim., 2003, 93, a) Cossy, J.; Bauer, D.; Bellosta, V. Tetrahedron 2002, 58, b) liver, J. E.; Doss, R. P.; Williamson,, T. R.; Carney, J. R.; DeVilbiss, E. D. Tetrahedron 2000, 56, Fujita, T.; Adachi, K. ; Kohara, T. ; Kiuchi, M. ; Chiba, K. ; Teshima, K.; Mishina, T. U.S. 1999, 88pp., Cont.-int-part of Appl. No. PCT/JP95/ CDEN: USXXAM US S2

3 General procedure for the Curtius rearrangement. To a solution of sodium azide (341 mg, 5.25 mmol), tetrabutylammonium bromide (72.0 mg, mmol), zinc triflate (II) (18.0 mg, 49.5 µmol) and carboxylic acid (1.50 mmol) in TF (15.0 ml) at 40 C, was added di-tert-butyldicarbonate (375 µl, 1.65 mmol). The resulting mixture was then stirred at 40 C (50 C for malonate derivatives). When the reaction is completed by GC analysis, a 10% solution of NaN 2 (30 ml) was added. The mixture was then diluted with ethyl acetate (30 ml), and the resulting mixture was stirred during 20 min at 25 C. The aqueous layer was extracted with ethyl acetate (3 x 25 ml) and the combined organic layers were washed with saturated N 4 Cl (2 x 30 ml), with saturated NaC 3 (2 x 30 ml) and brine (30 ml). The organic layer was dried over Na 2 S 4 and the solvent was removed under reduced pressure and the crude carbamate was purified by flash chromatography on silica gel with a pre-absorption on silica. NB. Although we have conducted this procedure on a 10 mmol scale without any problem, extreme care should be taken when carried out this reaction, as metal azides are known to be explosive. Synthesis of Acyl Azide N Adamantane acyl azide (1). To a solution of 1-adamantane carboxylic acid (540 mg, 3 mmol), sodium azide (682 mg, mmol) in TF (30 ml) was added di-tert-butyldicarbonate (750 µl, 3.3 mmol). Then the resulting mixture was stirred at 25 C. After 16 hours of reaction a 10% solution of NaN 2 (60 ml) was added. The mixture was then diluted with ethyl ether (60 ml), and the resulting mixture was stirred during 20 min at 25 C. The aqueous layer was extracted with ethyl ether (3 x 50 ml) and the combined organic layers were washed with water (2x60 ml), with saturated N 4 Cl (2x60 ml), with saturated NaC 3 (2x60 ml) and brine (60 ml). The organic layer was dried over Na 2 S 4 and the solvent was removed under reduced pressure. The crude acyl azide 1 (610 mg, 99%) was obtained as a white solid. The acyl azide readily decomposes upon flash chromatography, thus was characterized as the corresponding isocyanate (commercially available). A TF (15 ml) solution of crude acyl azide 1 was refluxed for 5 hours. After evaporation of the solvent, the crude material was purified by flash chromatography (5% EtAc/hexanes), providing the corresponding isocyanate (468 mg, 88%) as a white solid. R f 0.85 (20% EtAc/hexanes); 1 NMR (400 Mz, CDCl 3 ) 2.09 (s, 3), 1.88 (s, 6), 1.65 (m, 6); 13 C NMR (100 Mz, CDCl 3 ) (br), 55.6, 45.2, 35.6, Characterization of Carbamate Products 2 tert-butyl adamantan-1-yl-carbamate (2). The title compound was prepared from 1-adamantane carboxylic acid (270 mg, 1.50 mmol) according to the general procedure. The desired carbamate 2 (339 mg, 90%) was obtained as a white solid after flash chromatography (5% EtAc/hexanes). R f 0.62 (20% EtAc/hexanes); mp 101 C; 1 NMR (400 Mz, C 6 D 6, 70 C) 4.37 (s (br), 1), 2.04 (s (br), 3), 1.90 (s, 6), (m, 6), 1.41 (s, 9); 13 C NMR (100 Mz, C 6 D 6, 60 C) S3

4 154.1, 78.1, 50.5, 42.3, 36.8, 30.1, 28.7; IR 3324, 3268, 2904, 2850, 1684, 1360, 1164, 1027, 628 cm -1 ; MRS (ESI) calcd for for C N 2 Na [M+Na] + : Found: C 2 3 tert-butyl hexan-3-yl-carbamate (3). The title compound was prepared from 2-ethyl pentanoic acid (195 mg, 1.50 mmol) according to the general procedure. The desired carbamate 3 (285 mg, 94%) was obtained after flash chromatography (10% EtAc/hexanes), as a white solid. R f 0.59 (20% EtAc/hexanes); mp 47 C; 1 NMR (400 Mz, C 6 D 6, 70 C) 3.93 (s (br), 1), 3.63 (s (br), 1), 1.57 (s, 9), (m, 6), 0.92 (t, J = 7 z, 3), 0.88 (t, J = 7 z, 3); 13 C NMR (100 Mz, CDCl 3 ) 155.6, 78.2, 51.5, 37.0, 28.1, 28.0, 18.9, 13.7, 9.91; IR 3317, 2962, 2930, 2873, 1678, 1530, 1162, 663 cm -1 ; MRS (ESI) calcd for C N 2 Na [M+Na] + : Found: C 2 4 tert-butyl isobutylcarbamate 4. The title compound was prepared from isovaleric acid (176 µl, 1.50 mmol) according to the general procedure. The desired carbamate 4 (200 mg, 77%) was obtained after flash chromatography (10% EtAc/hexanes), as a colorless oil. R f 0.57 (20% EtAc/hexanes); 1 NMR (400 Mz, C 6 D 6, 70 C) 4.61 (s (br), 1), 2.91 (s (br), 2), 1.70 (septuplet, J = 7 z, 1), 1.42 (s (br), 9), 0.87 (d, J = 7 z 6); 13 C NMR (75 Mz, CDCl 3 ) 156.0, 78.8, 47.9, 28.8, 28.3, 19.9; IR 3356, 2961, 2931, 2872, 1688, 1512, 1164, 644 cm -1 ; MRS (ESI) calcd for C 9 19 N 2 Na [M+Na] + : Found: C 2 5 tert-butyl ((1S,3R)-3-acetyl-2,2-dimethylcyclobutyl)methylcarbamate (5). The title compound was prepared from 2-((1S,3R)-2,2-dimethyl-3-(2-oxopropyl)cyclopropyl)acetic acid (276 mg, 1.50 mmol) according to the general procedure. The desired carbamate 5 (240 mg, 68%) was obtained as a orange oil after flash chromatography (20% EtAc/hexanes). R f 0.50 (20% EtAc/hexanes); [ ] D 25 = (c, 0.1, CCl 3 ); 1 NMR (400 Mz, C 6 D 6, 70 C) 4.48 (s (br), 1), (m, 1), (m, 1), 2.10 (dd, J = 7, 4 z, 2), 1.82 (s, 3), 1.57 (s, 9), 0.99 (s, 3), 0.82 (s, 3), (m, 1), 0.63 (q, J = 9z, 1); 13 C NMR (75 Mz, CDCl 3 ) 209.2, 155.8, 79.0, 38.8, 37.0, 29.8, 28.5, 28.3, 25.6, 21.2, 17.2, 14.9; IR 3331, 3357, 2977, 1700, 1511, 1164, 754, 645 cm -1 ; MRS (ESI) calcd for C N 3 Na [M+Na] + : Found: C 2 6 tert-butyl 2,6-dimethylhept-5-enyl-carbamate (6). The title compound was prepared from citronellic acid (276 µl, 1.50 mmol) according to the general procedure. The desired carbamate 6 (290 mg, 80%) was obtained as a colorless oil after flash chromatography (5% EtAc/hexanes). R f 0.69 (20% EtAc/hexanes); 1 NMR (400 Mz, C 6 D 6, 70 C) (m, 1), 4.27 (s (br), 1), (m, 1), (m, 1), (m, 2), 1.75 (m, 3), 1.63 (s, 3), 1.55 (s, 9), (m, 1), (m, 1), (m, 1), 0.83 (d, J = 7z, 3); 13 C NMR (100 Mz, CDCl 3 ) 155.9, 131.2, 124.3, 78.7, 46.4, 34.2, 33.1, 28.3, 25.5, 25.2, 17.5, 17.2; IR 3356, 2967, 2917, 1690, 1169, 986, 664 cm -1 ; MRS (ESI) calcd for C N 2 [M+] + : Found: S4

5 C 2 7 tert-butyl 4-phenylbutylcarbamate (7). The title compound was prepared from phenylvaleric acid (267 mg, 1.50 mmol) according to the general procedure. The desired carbamate 7 (213 mg, 57%) was obtained as a colorless oil after flash chromatography (10% EtAc/hexanes). R f 0.50 (20% EtAc/hexanes); 1 NMR (400 Mz, C 6 D 6, 60 C) (m, 3), (m, 2), 3.98 (s (br), 1), (m, 2), 2.34 (t, J = 7 z, 2), 1.40 (s, 9), (m, 2), (m, 2); 13 C NMR (75 Mz, CDCl 3 ) 155.7, 141.9, 128.1, 128.0, 125.5, 78.7, 40.1, 35.2, 29.4, 28.3, 28.1; IR 3356, 2976, 2931, 2860, 1689, 1507, 1165, 1165, 748, 698 cm -1 ; MRS (ESI) calcd for C N 2 [M+] + : Found: C 2 8 tert-butyl (R)-3-((3R,5R,8S,9S,10S,14R,17R)-hexadecahydro-3-hydroxy-10-methyl-1-cyclopenta[ ]phenanthren-17-yl)butylcarbamate (8). The title compound was prepared from litocholic acid (544 mg, 1.50 mmol) according to the general procedure. The desired carbamate 8 (455 mg, 70%) was obtained as a white solid after precipitation with dichloromethane. R f 0.53 (5% Me/Dichloromethane); mp 181 C; [ ] 25 D = (c, 0.1, CCl 3 ); 1 NMR (400 Mz, DMS, 100 C) (m, 1), (m, 1), (m, 1), (m, 2), (m, 6), (m, 18), (m, 5), 0.90 (s, 9), 0.66 (s, 6); 13 C NMR (100 Mz, DMS) 175.2, 70.1, , 55.7, 42.4, 41.7, 36.3, 35.5, 35.3, 34.9, 34.3, 30.9, 30.8, 30.4, 27.9, 27.0, 26.3, 24.0, 23.4, 20.9, 20.6, 18.3, 14.2, 12.0; IR 3277, 2926, 2860, 2528, 1700, 1448, 1331, 1213, 1042, 1033, 687 cm -1 ; MRS (ESI) calcd for C N 3 Na [M+Na] + : Found: C 2 9 tert-butyl 1-phenylpropylcarbamate (9). The title compound was prepared from 1-phenyl butyric acid (246 mg, 1.50 mmol) according to the general procedure. The desired carbamate 9 (205 mg, 58%) was obtained as a white solid after flash chromatography (5% EtAc/hexanes then 10% EtAc/hexanes); R f 0.45 (20% EtAc/hexanes); mp 95 C; 1 NMR (300 Mz, CDCl 3 ) (m, 5), 4.54 (s (br), 1), 4.37 (s (br), 1), (m, 2), 1.37(s (br), 9), 0.66 (t, J = 7 z, 3); 13 C NMR (75 Mz, CDCl 3 ) 155.2, 142.8, 128.3, 126.9, 126.2, 79.0, 56.2, 29.7, 28.2, 10.6; IR 3356, 2965, 2872, 1675, 1522, 1163, cm -1 ; MRS (ESI) calcd for C N 2 [M+] + : Found: TBDPS TBDPS tert-butyl (R)-2-(tert-butyldiphenylsilanyloxy)-1-methyl)ethylcarbamate (11). The title compound was prepared from (2R)-methyl-3-tert-butyldiphenylsilanyloxypropionic acid (10) (343 mg, 1.00 mmol) according to the general procedure. The desired carbamate 11 (203 mg, 49%) was obtained as a colorless oil after flash chromatography (5% EtAc/hexanes then 10% S5

6 EtAc/hexanes); R f 0.55 (20% EtAc/hexanes); [ ] D = (c, 0.1, CCl 3 ); 1 NMR (400 Mz, C 6 D 6, 60 C) (m, 4), (m, 6), 4.36 (s (br), 1), (s (br), 1), 3.54 (dd, J = 10, 5 z, 1), 3.46 (dd, J = 10, 5 z, 1), 1.44 (s, 9), 1.11 (s, 9), 0.97 (d, J = 7 z, 3); 13 C NMR (100 Mz, CDCl 3 ) 155.3, 135.5, 133.4, 134.8, 129.7, 127.7, 79.0, 67.1, , 26.9, 19.3, 17.8; IR 3445, 3070, 2930, 2857, 1693, 1499, 1428, 1366, 1168, 1111, 823, 683 cm -1 ; MRS (ESI) calcd for C N 3 Si [M+] + : Found: The enantiomeric excess was determined to be 97.5% (79 : 1) by chiral SFC analysis (Chiracel D, 1mL/min, 0.5% Me, P = 130 mbar, T(oven) = 28 C, t r 27.8 (major), 30.9 (minor)). Me C 2 Me 12 tert-butyl 2-(ethoxycarbonyl)-4-phenylbutan-2-ylcarbamate (12). The title compound was prepared from 2-(ethoxycarbonyl)-2-methyl-4-phenylbutanoic acid (357 mg, 1.50 mmol) according to the general procedure at 50 C. The desired carbamate 12 (347 mg, 75%) was obtained as a colorless oil after flash chromatography (5% EtAc/hexanes then 10% EtAc/hexanes); R f 0.5 (20% EtAc/hexanes); 1 NMR (400 Mz, C 6 D 6, 60 C) (m, 5), 5.32 (s (br), 1), 3.86 (q, J = 7 z, 2), (m, 2), (m, 1), (m, 1), 1.52 (s, 3), 1.40 (s, 9), 0.89 (t, J = 7 z, 3); 13 C NMR (100 Mz, CDCl 3 ) 173.9, 153.9, 141.0, (2C), 125.6, 78.8, 61.0, 59.0, 38.2, 30.3, 28.0, 23.2, 13.8; IR 3426, 2978, 2935, 1712, 1495, 1365, 1164, 1057, 699 cm -1 ; MRS (ESI) calcd for C N 4 Na [M+Na] + : Found: C 2 Et Et 13 tert-butyl 3-(ethoxycarbonyl)hex-5-en-3-ylcarbamate (13). The title compound was prepared from 2-(ethoxycarbonyl)-2-ethylpent-4-enoic acid (300 mg, 1.50 mmol) according to the general procedure at 50 C. The desired carbamate (264 mg, 65%) was obtained as a colorless oil after flash chromatography (5% EtAc/hexanes then 10% EtAc/hexanes). R f 0.57 (20% EtAc/hexanes); 1 NMR (400 Mz, C 6 D 6, 60 C) (m, 1), 5.54 (s (br), 1), (m, 2), 3.91 (q, J = 7 z, 2), (m, 1), (m, 1), (m, 1), (m, 1), 1.40 (s, 9), 0.91 (t, J = 7z, 3), 0.80 (t, J = 7z, 3); 13 C NMR (100 Mz, CDCl 3 ) 173.1, 153.6, 132.5, 118.6, 78.7, 63.7, 61.3, 39.2, 28.1 (2C), 14.0, 7.98; IR 3431, 2978, 2936, 1714, 1490, 1168, 1066, 929, 665 cm -1 ; MRS (ESI) calcd for C N 4 Na [M+Na] + : Found: C 2 14 tert-butyl 3-(ethoxycarbonyl)-1-phenylhex-5-en-3-ylcarbamate (14). The title compound was prepared from 2-(ethoxycarbonyl)-2-phenethylpent-4-enoic acid (414 mg, 1.50 mmol) according to the general procedure. The desired carbamate 14 (312 mg, 60%) was obtained as a colorless oil after flash chromatography (5% EtAc/hexanes then 10% EtAc/hexanes). R f 0.59 (20% EtAc/hexanes); 1 NMR (400 Mz, C 6 D 6, 60 C) (m, 5), (m, 2), (m, 2), (m, 2), (m, 1), (m, 2), (m, 2), (m, 1), 1.40 (s, 9), 0.87 (t, J = 7z, 3); 13 C NMR (100 Mz, CDCl 3 ) 173.0, 153.6, 141.2, 132.3, 128.3, 128.2, 125.7, 118.7, 78.9, 63.1, 61,5, 39.8, 36.9, 30.5, 28.2, 14.1; IR 3426, 2978, 2932, 1713, 1489, 1164, 1029, 918, 699 cm -1 ; MRS (ESI) calcd for C N 4 [M+Na] + : Found: S6