1370
D. Enders, J. Han / 19 (2008) 1367–1371
at rt for 66 h. During this time, additional Et3SiH (28.5 mL,
178 mmol) and BF3ꢃOEt2 (22.0 mL, 178 mmol) were added to com-
plete the reaction. The reaction mixture was washed with satu-
rated aqueous NaHCO3 solution, brine, and then dried over
Na2SO4. Concentration and chromatography (CHCl3/AcOEt = 2:1)
1052, 849, 763, 708, 633, 582, 525. 1H NMR (300 MHz, CDCl3):
1H NMR (300 MHz, CDCl3): 0.00 (s, 9H, Si(CH3)3), 2.08–2.20 (m,
1H, C(O)CH2CHH), 2.82–3.01 (m, 2H, C(O)CH2CH), 3.31–3.42 (m,
1H, C(O)CH2CHH), 6.20 (d, J = 8.5 Hz, 1H, NCH), 7.34–7.36 (m, 2H,
Ph), 7.40–7.45 (m, 5H, Ph), 7.51–7.54 (m, 3H, Ph), 7.64–7.67 (m,
3H, Ph), 7.76–7.79 (m, 2H, Ph), 8.95 (s, 1H, NCHN). 13C NMR
(75 MHz, CDCl3): 1.4, 21.1, 29.8, 68.1, 121.2, 128.0, 128.5, 128.6,
128.8, 129.0, 129.2, 130.2, 135.4, 136.6, 139.7, 140.1, 162.5. MS
(ESI): m/z = 440.1 (100, M+), 350.5 (15), 87.3 (100, BF4ꢀ). Anal.
gave 13 as a colorless solid (4.37 g, 78%). ½a D23
¼ þ25:5 (c 1.01,
ꢂ
CHCl3); 1H NMR (300 MHz, CDCl3): 1.74–1.86 (m, 1H,
C(O)CH2CHH), 2.09–2.21 (m, 1H, C(O)CH2CHH), 2.30–2.36 (m, 2H,
C(O)CH2), 3.76 (d, J = 10.4 Hz, 1H, CHPh2), 4.37–4.45 (m, 1H,
NCH), 5.44 (br s, 1H, NH), 7.22–7.30 (m, 10H, Ph). 13C NMR
(75 MHz, CDCl3): 26.4, 30.1, 57.5, 58.4, 126.9, 127.1, 127.8, 128.7,
129.0, 140.6, 141.5, 177.2.
Calcd for C27H30N3OSiþBF ꢀ: C, 61.48; H, 5.73; N, 7.97. Found: C,
4
61.52; H, 5.581; N, 7.95.
4.2.11. (S)-5-Benzhydryl-2-phenyl-6,7-dihydro-5H-pyrrolo-
[2,1-c][1,2,4]triazol-2-ium tetrafluoroborate 9
4.2.7. General procedure for the synthesis of the precatalysts
A 10 mL round-bottomed flask was charged with the lactam
(1 mmol) and CH2Cl2 (10 mL). Trimethyloxonium tetrafluoroborate
(0.16 g, 1.1 mmol) was added and the reaction mixture was stirred
overnight at room temperature. Phenylhydrazine (0.11 mL,
1.1 mmol) was added to the solution and stirred overnight. The sol-
vent was removed in vacuo and the product was used without fur-
ther purification. Trimethyl orthoformate (10 mL) was added and
the reaction mixture was heated to 80 °C and stirred at this tem-
perature overnight. The solvent was removed in vacuo and the
product was precipitated from ethyl acetate to give an off white/
yellow powder. Recrystallization from hot MeOH afforded 8a–c
and 9 as a colorless crystalline solid.
Yield (0.37 g, 85%). Mp: 180 °C. ½a D23
¼ þ14:5 (c 1.01, CHCl3); IR
ꢂ
(KBr):
m = 3440, 3166, 3061, 3030, 2960, 1814, 1592, 1522, 1495,
1450, 1387, 1291, 1202, 1069, 977, 921, 832, 764, 703, 630, 607,
588, 520, 493. 1H NMR (300 MHz, CDCl3): 2.49–2.60 (m, 1H,
C(O)CH2CHH), 2.84–2.97 (m, 1H, C(O)CH2CHH), 3.11–3.16 (m, 2H,
C(O)CH2), 4.28/4.31 (d, J = 10.9 Hz, 1H, CHPh2), 5.83–5.91 (m, 1H,
NCH), 7.24–7.50 (m, 15H, Ph), 7.95 (s, 1H, NCHN). 13C NMR
(75 MHz, CDCl3): 21.1, 32.4, 55.4, 64.0, 121.4, 127.7, 127.8, 128.2,
128.3, 129.2, 129.7, 129.9, 130.7, 135.3, 135.7, 138.8, 139.6,
162.5. MS (ESI): m/z = 352.2 (100, M+), 274.4 (5), 87.3 (100,
BF4ꢀ); Anal. Calcd for C27H30N3OSiþBF ꢀ: C, 65.62; H, 5.05; N,
4
9.57. Found: C, 65.47; H, 5.21; N, 9.55.
4.2.8. (S)-5-((tert-Butyldimethylsilyloxy)diphenylmethyl)-2-
phenyl-6,7-dihydro-5H-pyrrolo[2,1-c][1,2,4]triazol-2-ium
tetrafluoroborate 8a
4.3. Benzoin reaction
A dry flask was charged with the precatalyst (0.1 mmol,
10 mol %), absolute toluene (1 mL), KHMDS in toluene (0.5 M,
0.2 mL), and then the aromatic aldehyde (1 mmol) was added
dropwise at room temperature under argon. The reaction mixture
was stirred for 8 h, then the reaction mixture was directly purified
by chromatography (silica gel, ether/pentane; 1:4) to give the de-
sired benzoins as colorless solids or pale yellow oils. The 1H NMR
spectra were in accordance with those reported in the literature.13
Yield (0.45 g, 80%). Mp: 186 °C. ½a D23
¼ ꢀ137:5 (c 1.01, CHCl3); IR
ꢂ
(KBr):
m = 3415, 3105, 2953, 2930, 2889, 2854, 1593, 1516, 1493,
1468, 1445, 1385, 1064, 873, 836, 779, 706. 1H NMR (300 MHz,
CDCl3): ꢀ0.35 (s, 3H, SiCH3), ꢀ0.32 (s, 3H, SiCH3), 0.94 (s, 9H,
SiC(CH3)3), 1.60–1.71 (m, 1H, C(O)CH2CHH), 2.72–2.93 (m, 2H,
C(O)CH2CH), 3.12–3.27 (m, 1H, C(O)CH2CHH), 6.10 (d, J = 7.7 Hz,
1H, NCH), 7.13–7.15 (m, 2H, Ph), 7.31–7.36 (m, 2H, Ph), 7.37–
7.47 (m, 4H, Ph), 7.50–7.55 (m, 5H, Ph), 7.65–7.71 (m, 2H, Ph),
9.06 (s, 1H, NCHN). 13C NMR (75 MHz, CDCl3): ꢀ3.6 and ꢀ3.5,
18.6, 20.7, 26.0, 29.5, 66.3, 82.1, 121.4, 127.9, 128.4, 128.9, 129.0,
130.1, 130.9, 135.3, 136.9, 139.0, 140.0, 163.4. MS (ESI): m/z =
482.2 (100, M+), 350.4 (5), 87.3 (100, BF4ꢀ); Anal. Calcd for
Acknowledgments
This work was supported by the Deutsche Forschungsgemein-
schaft (Priority Programme 1179 Organocatalysis) and the Fonds
der Chemischen Industrie. We thank Degussa AG, BASF AG, Bayer
AG and Wacker Chemie for the donation of chemicals. We thank
Alexander Henseler and Dr. Arun Narine for their help in the prep-
aration of the manuscript.
C27H30N3OSiþBF ꢀ: C, 63.27; H, 6.37; N, 7.38. Found: C, 63.75; H,
4
6.325; N, 7.40.
4.2.9. (S)-2-Phenyl-5-(2-(trimethylsilyloxy)propan-2-yl)-6,7-
dihydro-5H-pyrrolo[2,1-c][1,2,4]triazol-2-ium tetra-
fluoroborate 8b
References
Yield (0.25 g, 63%). Mp: 110 °C. ½a D23
¼ ꢀ46:3 (c 1.01, CHCl3); IR
ꢂ
1. Reviews: (a) Enders, D.; Niemeier, O.; Henseler, A. Chem. Rev. 2007, 107, 5506;
(b) Marion, N.; Diez-Gonzalez, S.; Nolan, S. P. Angew. Chem. 2007, 119, 3046;
Marion, N.; Diez-Gonzalez, S.; Nolan, S. P. Angew. Chem., Int. Ed. 2007, 46, 2988;
(c) Zeitler, K. Angew. Chem. 2005, 117, 7674; Zeitler, K. Angew. Chem., Int. Ed.
2005, 44, 7506; (d) Christmann, M. Angew. Chem. 2005, 117, 2688; (e)
Christmann, M. Angew. Chem., Int. Ed. 2005, 44, 2632; (f) Enders, D.;
Balensiefer, T. Acc. Chem. Res. 2004, 37, 534.
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3. Seebach, D. Angew. Chem. 1979, 91, 259; Seebach, D. Angew. Chem., Int. Ed. 1979,
18, 239.
4. (a) Sohn, S. S.; Rosen, E. L.; Bode, J. W. J. Am. Chem. Soc. 2004, 126, 14370; (b)
Burstein, C.; Glorius, F. Angew. Chem. 2004, 116, 6331; (c) Burstein, C.; Glorius,
F. Angew. Chem., Int. Ed. 2004, 43, 6205.
5. (a) Reynolds, N. T.; Read de Alaniz, J.; Rovis, T. J. Am. Chem. Soc. 2004, 126, 9518;
(b) Chow, K. Y.-K.; Bode, J. W. J. Am. Chem. Soc. 2004, 126, 8126.
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A.; Kissling, R. M.; Nolan, S. P. Org. Lett. 2002, 4, 3583.
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914.
8. (a) Zhou, H. Y.; Campbell, E. J.; Nguyen, S. T. Org. Lett. 2001, 3, 2229; (b) Wu, J.;
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(KBr):
m = 3424, 3193, 2977, 2898, 1592, 1532, 1470, 1438, 1400,
1249, 1187, 1144, 1060, 976, 882, 847, 765, 685, 520. 1H NMR
(300 MHz, CDCl3): 0.0 (s, 9H, Si(CH3)3), 1.24 and 1.40 (s, 3H,
C(CH3)2), 2.62–2.68 (m, 1H, C(O)CH2CHH), 2.83–2.96 (m, 1H,
C(O)CH2CHH), 3.05–3.12 (m, 2H, C(O)CH2), 4.79 (dd, J = 8.0,
0.9 Hz, 1H, NCH), 7.48–7.50 (m, 3H, Ph), 7.76–7.80 (m, 2H, Ph),
9.89 (s, 1H, NCHN). 13C NMR (75 MHz, CDCl3): 2.0, 22.0, 26.0 and
26.9, 29.3, 70.2, 74.7, 120.8, 130.2, 130.8, 137.2, 163.5. MS (ESI):
m/z = 316.1 (100, M+), 226.2 (15), 87.3 (100, BF4ꢀ); Anal. Calcd
for C27H30N3OSiþBF ꢀ: C, 50.63; H, 6.50; N, 10.42. Found: C,
4
50.88; H, 6.890; N, 10.47.
4.2.10. (S)-5-(Diphenyl(trimethylsilyloxy)methyl)-2-phenyl-
6,7-dihydro-5H-pyrrolo[2,1-c][1,2,4]triazol-2-ium tetra-
fluoroborate 8c
Yield (0.3 g, 68%). Mp: 215 °C. ½a D23
¼ ꢀ130:2 (c 1.01, CHCl3); IR
ꢂ
(KBr):
m = 3171, 3065, 2958, 1594, 1520, 1444, 1394, 1254, 1193,