Electronic Supplementary Material (ESI) for Organic & Biomolecular Chemistry. This journal is The Royal Society of Chemistry 2015 Supporting Information DBU-Mediated Metal-Free Oxidative Cyanation of α-amino Carbonyl Compounds: Using Molecular Oxygen as the Oxidant Lei Li, Qian Wang, Pei Liu, Hua Meng, Xing-Lan Kan, Qun Liu, and Yu-Long Zhao,*, Department of Chemistry, Northeast Normal University, Changchun, 130024, P. R. China Zhejiang Sucon Silicone Co.,Ltd., Shaoxing, 312088, P. R. China e-mail: zhaoyl351@nenu.edu.cn Table of contents I. General Information...S2 II. General Procedure for the Preparation of 3...S3-S9 III. General Procedure for the Preparation of 6... S10-S11 IV. Crystal ORTEP drawing of compound 3a...S12 V. Copies of 1 H NMR and 13 C NMR spectra of compounds 3, 4 and 6...S13-S30 S1
I. General Information All reagents were commercial and were used without further purification. Chromatography was carried on flash silica gel (300-400 mesh). All reactions were monitored by TLC, which was performed on precoated aluminum sheets of silica gel 60 (F254). Melting points were uncorrected. Unless noted, the 1 H NMR spectra were recorded at 400 MHz and 500 MHz in CDCl 3 and the 13 C NMR spectra were recorded at 125 MHz in CDCl 3 with TMS as internal standard. All coupling constants (J values) were reported in Hertz (Hz). High-resolution mass spectra (HRMS) were obtained using a Bruker microtof II focus spectrometer (ESI). The compound 3a was glued on a glass fiber. Data were collected at 293K using graphite-monochromated Mo Kα radiation (λ = 0.71073Å) and IP technique in the range 2.19 < θ < 27.48. Empirical absorption correction was applied. The structures were solved by the direct method and refined by the full-matrix least-squares method on F2 using the SHELXS 97 crystallographic software package. Anisotropic thermal parameters were used to refine all non-hydrogen atoms. Hydrogen atoms were located from difference Fourier maps. S2
II. General Procedure for the Preparation of 3 (3a as Example): R O O H N DBU (1.5 equiv) N Ar + TMSCN Ar DMF, rt, 4-10 min CN R 1 2 3 To a solution of (E)-4-(4-chlorophenyl)-1-(p-tolylamino)but-3-en-2-one 1a (0.2 mmol, 57.1 mg) and TMSCN 2 (0.30 mmol, 0.040 ml) in DMF (1.5 ml) was added DBU (0.3 mmol, 0.045 ml). Then the reaction mixture was stirred at room temperature in open air for 5 min. After 1a was consumed (monitored by TLC), the reaction mixture was poured into water (50 ml) and extracted with CH 2 Cl 2 (10 ml 3). The combined organic extracts were dried over anhydrous Na 2 SO 4, filtered and concentrated under reduced pressure to yield the corresponding crude product, which was purified by chromatography (silica gel, petroleum ether/acetone = 10/1, v/v) to give 3a (44.4 mg, 72%) as a yellow solid. (1E,3E)-4-(4-chlorophenyl)-2-oxo-N-(p-tolyl)but-3-enimidoyl cyanide (3a): Yellow solid; m.p. 107-109 o C; 1 H NMR (CDCl 3, 500 MHz) δ: 7.91 (d, J = 16.0 Hz, 1H), 7.83 (d, J = 16.0 Hz, 1H), 7.63 (d, J = 8.5 Hz, 2H), 7.50 (d, J = 8.5 Hz, 2H), 7.42 (d, J = 8.5 Hz, 2H), 7.35 (d, J = 8.5 Hz, 2H), 2.45 (s, 3H); 13 CNMR (CDCl 3, 125 MHz) δ: 183.5, 145.4, 143.3, 142.2, 137.4, 135.8, 132.8, 130.3, 130.2, 129.4, 123.0, 118.4, 110.6, 21.6; IR (KBr) ν: 2921, 2215, 1618, 1600, 1556, 1445, 1319, 1108, 1060 cm -1 ; HRMS (ESI-TOF)calcd for C 18 H 13 ClN 2 ONa + ([M + Na] + ): 331.0609, found: 331.0620. (1E,3E)-2-oxo-N-(p-tolyl)-4-(4-(trifluoromethyl)phenyl)but-3-enimidoyl cyanide (3b): S3
O N CN F 3 C Yellow solid; m.p. 135-137 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.94 (d, J = 4.0 Hz, 2H), 7.79 (d, J = 8.0 Hz, 2H), 7.69 (d, J = 8.5 Hz, 2H), 7.53 (d, J = 8.0 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H), 2.46 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.5, 144.7, 143.2, 142.5, 137.6, 135.4, 132.6 (q, J = 32.7 Hz), 130.3, 129.1, 126.0 (q, J = 3.6 Hz), 123.7 (q, J = 270.7 Hz), 123.2, 120.2, 110.6, 21.6; IR (KBr) ν: 2926, 2211, 1608, 1607, 1550, 1324, 1117, 1066 cm -1 ; HRMS (ESI-TOF)calcd for C 19 H 14 F 3 N 2 O + ([M + H] + ): 343.1053, found: 343.1049. (1E,3E)-4-(2-chlorophenyl)-2-oxo-N-(p-tolyl)but-3-enimidoyl cyanide (3c): Yellow solid; m.p. 118-120 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 8.39 (d, J = 16.0 Hz, 1H), 7.85-7.81 (m, 2H), 7.50 (d, J = 8.5 Hz, 2H), 7.46 (dd, J = 8.0 Hz, 1.0 Hz, 1H), 7.39-7.32 (m, 4H), 2.45 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.4, 143.2, 142.5, 142.3, 136.2, 135.6, 132.5, 132.0, 130.4, 130.3, 128.0, 127.1, 123.0, 120.3, 110.6, 21.5; IR (KBr) ν: 3032, 2217, 1663, 1595, 1328, 1272, 1208 cm -1 ; HRMS (ESI-TOF)calcd for C 18 H 14 ClN 2 O + ([M + H] + ): 309.0789, found: 309.0798. (1E,3E)-2-oxo-N,4-dip-tolylbut-3-enimidoyl cyanide (3d): Yellow solid; m.p. 133-135 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.96 (d, J = 16.0 Hz, 1H), 7.81 (d, J = 16.0 Hz, 1H), 7.60 (d, J = 8.0 Hz, 2H), 7.48 (d, J = 8.5 Hz, 2H), 7.34 (d, J = 8.0 Hz, 2H), 7.25 (d, J = 8.5 Hz, 2H), 2.45 (s, 3H), 2.41 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.6, 147.2, 143.5, S4
142.3, 141.8, 136.2, 131.6, 130.2, 129.8, 129.2, 122.8, 116.8, 110.7, 21.7, 21.5; HRMS (ESI-TOF) calcd for C 19 H 17 N 2 O + ([M + H] + ): 289.1335, found: 289.1337. (1E,3E)-4-(4-methoxyphenyl)-2-oxo-N-p-tolylbut-3-enimidoyl cyanide (3e): O N CN MeO Yellow solid; m.p. 112-114 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.94 (d, J = 16.0 Hz, 1H), 7.72 (d, J = 16.0 Hz, 1H), 7.66 (d, J = 8.5 Hz, 2H), 7.46 (d, J = 8.5 Hz, 2H), 7.34 (d, J = 8.0 Hz, 2H), 6.95 (d, J = 9.0 Hz, 2H), 3.87 (s, 3H), 2.44 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.4, 162.4, 146.9, 143.5, 141.7, 136.4, 131.1, 130.2, 127.1, 122.7, 115.4, 114.5, 110.7, 55.5, 21.5; IR (KBr) ν: 2960, 2930, 2217, 1730, 1663, 1258, 1170, 1020 cm -1 + ; HRMS (ESI-TOF) calcd for C 19 H 17 N 2 O 2 ([M + H] + ): 305.1285, found: 305.1286. (1E,3E)-2-oxo-4-phenyl-N-(p-tolyl)but-3-enimidoyl cyanide (3f): Yellow solid; m.p. 90-92 o C; 1 H NMR (CDCl 3, 500 MHz) δ: 7.97 (d, J = 16.0 Hz, 1H), 7.85 (d, J = 16.0 Hz, 1H), 7.69 (d, J = 7.5 Hz, 2H), 7.50 (d, J = 8.0 Hz, 2H), 7.44-7.46 (m, 3H), 7.34 (d, J = 8.0 Hz, 2H), 2.45 (s, 3H); 13 C NMR (CDCl 3, 125 MHz) δ: 183.6, 146.9, 143.4, 142.0, 135.9, 134.3, 131.4, 130.2, 129.0, 129.0, 122.9, 117.9, 110.6, 21.5; IR (KBr) ν: 2962, 2938, 2218, 1738, 1670, 1261, 1176, 1032 cm -1 ; HRMS (ESI-TOF) calcd for C 18 H 15 N 2 O + ([M + H] + ): 275.1179, found: 275.1179. (1E,3E)-4-(furan-2-yl)-2-oxo-N-(p-tolyl)but-3-enimidoyl cyanide (3g): S5
Yellow solid; m.p. 146-148 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.70 (s, 2H), 7.58 (s, 1H), 7.49 (d, J = 8.5 Hz, 2H), 7.34 (d, J = 8.5 Hz, 2H), 6.84 (d, J = 3.5 Hz, 1H), 6.56 (dd, J = 3.5, 1.6 Hz, 1H), 2.44 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.5, 151.4, 146.0, 143.4, 141.9, 135.8, 132.2, + 130.2, 122.9, 118.3, 115.5, 113.1, 110.7, 21.5; HRMS (ESI-TOF) calcd for C 16 H 13 N 2 O 2 ([M + H] + ): 265.0972, found: 265.0977. (1E,3E)-2-oxo-4-(thiophen-2-yl)-N-(p-tolyl)but-3-enimidoyl cyanide (3h): Yellow solid; m.p. 133-135 o C; 1 H NMR (CDCl 3, 500 MHz) δ: 2.44 (s, 3H), 7.12 (dd, J = 3.5, 5.0 Hz, 1H), 7.34 (d, J = 8.0 Hz, 2H), 7.45 (d, J = 2.0 Hz, 1H), 7.48 (d, J = 8.5 Hz, 2H), 7.50 (d, J = 5.0 Hz, 1H), 7.60 (d, J = 16.0 Hz, 1H), 8.07 (d, J = 15.5 Hz, 1H); 13 C NMR (CDCl 3, 125 MHz) δ: 183.2, 143.4, 141.9, 140.0, 139.1, 135.9, 133.5, 130.5, 130.2, 128.6, 122.9, 116.8, 110.7, 21.5; IR (KBr) ν: 2926, 2214, 1665, 1582, 1420, 1213, 1001 cm -1 ; HRMS (ESI-TOF) calcd for C 16 H 13 N 2 OS + ([M + H] + ): 281.0743, found: 281.0743. (1E,3E)-4-(naphthalen-2-yl)-2-oxo-N-p-tolylbut-3-enimidoyl cyanide (3i): Yellow solid; m.p. 176-178 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 8.13 (d, J = 15.5 Hz, 1H), 8.09 (s, 1H), 7.95 (d, J = 16.0 Hz, 1H), 7.92-7.82 (m, 4H), 7.57-7.53 (m, 2H), 7.51 (d, J = 8.5 Hz, 2H), 7.35 (d, J = 8.0 Hz, 2H), 2.45 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.5, 147.0, 143.4, 141.9, 136.1, 134.7, 133.2, 131.9, 130.2, 128.8, 127.8, 127.7, 126.9, 123.7, 122.9, 118.0, 110.7, 21.5. Two carbon is not visible due to overlapping peaks; IR (KBr) ν: 2920, 2217, 1666, 1598, 1567, 1363, 1302, 1200, 1002 cm -1 ; HRMS (ESI-TOF) calcd for C 22 H 17 N 2 O + ([M + H] + ): 325.1335, found: 325.1336. S6
(1E,3E,5E)-2-oxo-6-phenyl-N-(p-tolyl)hexa-3,5-dienimidoyl cyanide (3j): O N CN Yellow solid; m.p. 160-162 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.74 (dd, J = 15.5, 11.0 Hz, 1H), 7.52 (d, J = 7.5 Hz, 2H), 7.47 (d, J = 8.5 Hz, 2H), 7.41-7.35 (m, 4H), 7.33 (d, J = 8.0 Hz, 2H), 7.12 (d, J = 15.5 Hz, 1H), 7.07-7.02 (m, 1H), 2.44 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.6, 146.9, 144.3, 143.4, 141.9, 135.9, 135.7, 130.2, 129.8, 128.9, 127.6, 126.7, 122.9, 121.3, 110.7, 21.5; HRMS (ESI-TOF) calcd for C 20 H 17 N 2 O + ([M + H] + ): 301.1335, found: 301.1327. (1E,3E)-N,4-bis(4-chlorophenyl)-2-oxobut-3-enimidoyl cyanide (3k): Yellow solid; m.p. 148-150 o C; 1 H NMR (CDCl 3, 500 MHz) δ: 7.42 (d, J = 8.0 Hz, 2H), 7.46 (d, J = 8.5 Hz, 2H), 7.52 (d, J = 8.5 Hz, 2H), 7.63 (d, J = 8.0 Hz, 2H), 7.78 (d, J = 16.0 Hz, 1H), 7.92 (d, J = 16.0 Hz, 1H); 13 C NMR (CDCl 3, 125 MHz) δ: 183.0, 146.0, 144.2, 137.7, 137.6, 136.8, 132.6, 130.2, 129.9, 129.2, 123.7, 118.0, 110.0; IR (KBr) ν: 2923, 2208, 1668, 1607, 1487, 1335, 1092 cm -1 ; HRMS (ESI-TOF) calcd for C 17 H 11 Cl 2 N 2 O + ([M + H] + ): 329.0243, found: 329.0257. (1E,3E)-4-(4-chlorophenyl)-2-oxo-N-phenylbut-3-enimidoyl cyanide (3l): O N CN Cl Yellow solid; m.p. 165-167 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.93 (d, J = 16.0 Hz, 1H), 7.82 (d, J = 16.0 Hz, 1H), 7.64 (d, J = 8.5 Hz, 2H), 7.57-7.54 (m, 2H), 7.50-7.47 (m, 3H), 7.42 (d, J = 8.5 Hz, 2H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.2, 146.0, 145.8, 137.6, 137.5, 132.6, 130.6, 130.2, S7
129.6, 129.4, 122.0, 118.1, 110.1; IR (KBr) ν: 2220, 1728, 1674, 1604, 1564, 1332.67, 1208, 993 cm -1 ; HRMS (ESI-TOF) calcd for C 17 H 12 ClN 2 O + ([M + H] + ): 295.0633, found: 295.0626. (1E,3E)-4-(4-chlorophenyl)-2-oxo-N-(m-tolyl)but-3-enimidoyl cyanide (3m): O N CN Cl Yellow solid; m.p. 132-134 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.92 (d, J = 16.0 Hz, 1H), 7.81 (d, J = 16.0 Hz, 1H), 7.63 (d, J = 8.5 Hz, 2H), 7.45-7.40 (m, 3H), 7.29 (d, J = 5.5 Hz, 3H), 2.45 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.3, 146.0, 145.7, 139.7, 137.5, 137.2, 132.7, 131.5, 130.2, 129.4, 129.3, 122.8, 118.9, 118.2, 110.2, 21.3; IR (KBr) ν: 2922, 2217, 1667, 1598, 1563, 1329, 994 cm -1 ; HRMS (ESI-TOF) calcd for C 18 H 14 ClN 2 O + ([M + H] + ): 309.0789, found: 309.0791. (1E,3E)-4-(4-chlorophenyl)-N-(4-methoxyphenyl)-2-oxobut-3-enimidoyl cyanide (3n): O N CN OMe Cl Yellow solid; m.p. 153-155 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 7.88 (d, J = 16.0 Hz, 1H), 7.84 (d, J = 16.0 Hz, 1H), 7.79 (d, J = 9.0 Hz, 2H), 7.62 (d, J = 8.5 Hz, 2H), 7.41 (d, J = 8.5 Hz, 2H), 7.05 (d, J = 9.0 Hz, 2H), 3.92 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 183.9, 162.9, 144.8, 138.2, 137.2, 132.9, 132.3, 130.1, 129.3, 126.8, 118.5, 114.9, 111.5, 55.8; IR (KBr) ν: 2917, 2208, 1667, 1608, 1535, 1312, 1271, 1167, 993 cm -1 + ; HRMS (ESI-TOF) calcd for C 18 H 14 ClN 2 O 2 ([M + H] + ): 325.0738, found: 325.0733. S8
(E)-4-(4-chlorophenyl)-2-oxo-N-(p-tolyl)but-3-enamide (4a): Yellow solid; m.p. 143-145 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 8.93 (s, 1H), 7.94 (d, J = 16.0 Hz, 1H), 7.84 (d, J = 16.0 Hz, 1H), 7.62 (d, J = 8.5 Hz, 2H), 7.57 (d, J = 8.5 Hz, 2H), 7.41 (d, J = 8.5 Hz, 2H), 7.19 (d, J = 8.0 Hz, 2H), 2.34 (s, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 185.4, 158.4, 146.9, 137.6, 134.9, 133.9, 132.7, 130.3, 129.6, 129.3, 119.7, 118.3, 20.9; HRMS (ESI-TOF) calcd + for C 17 H 15 ClNO 2 ([M + H] + ): 300.0786, found: 300.0785. S9
III. General Procedure for the Preparation of 6 (6a as Example): R 1 O NH 2 N N R 2 NaOAc (1.2 eq) + CN AcOH, 120 0 C NH 2 N 3 6 CN R 1 To a solution of (1E,3E)-4-(4-chlorophenyl)-2-oxo-N-(p-tolyl)but-3-enimidoyl cyanide 3a (0.20 mmol, 61.6 mg) in AcOH (2 ml) was added benzene-1,2-diamine (0.24 mmol, 25.9 mg) and NaOAc (0.24 mmol, 19.7 mg). Then the reaction mixture was stirred at 120 o C for 10 min. After 3a was consumed (monitored by TLC), the reaction mixture was poured into water (50 ml) and extracted with CH 2 Cl 2 (10 ml 3). The combined organic extracts were dried over anhydrous Na 2 SO 4, filtered and concentrated under reduced pressure to yield the corresponding crude product, which was purified by chromatography (silica gel, petroleum ether/acetone = 10/2, v/v) to give 6a (53.5 mg, 92%) as a yellow solid. (E)-3-(4-Chlorostyryl)quinoxaline-2-carbonitrile (6a): Yellow solid; m.p. 173-175 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 8.13 (d, J = 15.5 Hz, 1H), 8.08 (t, J = 8.5 Hz, 2H), 7.89 (t, J = 8.0 Hz, 1H), 7.79 (t, J = 8.0 Hz, 1H), 7.62 (d, J = 8.5 Hz, 2H), 7.60 (d, J = 15.5 Hz, 1H), 7.39 (d, J = 8.0 Hz, 2H); 13 C NMR (125 MHz, CDCl 3 ) δ: 150.2, 142.7, 140.9, 138.4, 135.8, 133.8, 133.5, 130.9, 129.6, 129.3, 129.2, 129.2, 129.1, 120.8, 115.6; IR (KBr) ν: 2221, 1615, 1535, 1456, 1355, 1228, 951, 860, 750, 718 cm -1 ; HRMS (ESI-TOF) calcd for + C 17 H 11 ClN 3 ([M + H] + ): 292.0636, found: 292.0636. (E)-3-Styrylquinoxaline-2-carbonitrile (6f): S10
Yellow solid; m.p. 172-174 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 8.18 (d, J = 15.5 Hz, 1H), 8.08 (q, J = 8.5 Hz, 2H), 7.88 (t, J = 8.0 Hz, 1H), 7.77 (t, J = 7.5 Hz, 1H), 7.69 (d, J = 7.5 Hz, 2H), 7.64 (d, J = 16.0 Hz, 1H), 7.44-7.37 (m, 3H); 13 C NMR (125 MHz, CDCl 3 ) δ: 150.5, 142.7, 140.8, 139.9, 135.3, 133.4, 130.7, 130.0, 129.5, 129.2, 129.1, 128.9, 128.0, 120.2, 115.6; HRMS (ESI-TOF) + calcd for C 17 H 12 N 3 ([M + H] + ): 258.1026, found: 258.1031. (E)-3-(2-(Thiophen-2-yl)vinyl)quinoxaline-2-carbonitrile (6h): Yellow solid; m.p. 184-186 o C; 1 H NMR (500 MHz, CDCl 3 ) δ: 8.28 (d, J = 15.0 Hz, 1H), 8.04 (d, J = 9.0 Hz, 2H), 7.85 (t, J = 7.5 Hz, 1H), 7.75 (t, J = 7.5 Hz, 1H), 7.39 (d, J = 15.0 Hz, 1H), 7.39-7.36 (m, 2H), 7.09 (t, J = 4.0 Hz, 1H); 13 C NMR (125 MHz, CDCl 3 ) δ: 150.4, 142.8, 140.9, 140.7, 133.4, 132.3, 130.6, 130.4, 129.5, 129.1, 128.8, 128.2, 128.1, 119.2, 115.5; IR (KBr) ν: 2219, 1606, 1510.40, 1355, 1203, 958, 864, 756, 708 cm -1 ; HRMS (ESI-TOF) calcd for C 15 H 10 N 3 S + ([M + H] + ): 264.0590, found: 264.0591. S11
IV. Crystal ORTEP drawing of compound 3a: S12
V. Copies of 1 H NMR and 13 C NMR spectra of compounds 3, 4 and 6: Figure 1. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3a. S13
Figure 2. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3b. S14
Figure 3. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3c. S15
Figure 4. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3d. S16
Figure 5. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3e. S17
Figure 6. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3f. S18
Figure 7. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3g. S19
Figure 8. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3h. S20
Figure 9. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3i. S21
Figure 10. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3j. S22
Figure 11. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3k. S23
Figure 12. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3l. S24
Figure 13. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3m. S25
Figure 14. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 3n. S26
Figure 15. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 4a. S27
Figure 16. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 6a. S28
Figure 17. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 6f. S29
Figure 18. 1 H- (upper) and 13 C-NMR (lower) spectra of compound 6h. S30