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G. Delogu et al. / Tetrahedron: Asymmetry 9 (1998) 2819–2826
3.9. 1,11-Bis(methoxy)-N-(1-phenylethyl)-dibenzo[d,f][1,3,2]dithiophosphepin-6-amine, 6-sulfide 15
A solution of (S)-α-methylbenzylamine (1.2 g, 10 mmol) in dry pyridine (10 mL) was added to a cold
solution of thiophosphoryl chloride (1.66 g, 9.8 mmol) in pyridine (10 mL). The reaction mixture was
stirred at 0°C for 2 h and 1 h at rt. The heterogeneous mixture was treated with a 5% solution of H2SO4
(100 mL) and then with H2O. The organic phase was extracted with CH2Cl2 (3×20mL) to give (S)-α-
methylbenzyl dichlorophosphorothioamidate 16 (2.36 g, 95%). To a solution of racemic dimercaptan 1
(2.5 g, 9.0 mmol) in pyridine (30 mL) a solution of 16 (2.36 g, 9.28 mmol) was added dropwise at rt.
After 4 h of refluxing, the reaction was cooled and treated with a 10% solution of H2SO4 (100 mL). After
addition of H2O (100 mL), the organic phase was extracted with CH2Cl2 (3×50 mL) to give a solid after
evaporation that was purified by flash chromatography using a 1:2 mixture of CH2Cl2:petroleum ether
1
as the eluent (1.17 g, 20%). One diastereomer: H NMR δ 1.66 (d, J=6.6 Hz, 3H), 3.70, (s, 3H), 4.02
1
(m, 1H), 4.53 (m, 1H), 7.10–7.5 (series of m, Ar, 11H). One diastereomer: H NMR δ 1.70 (d, J=6.6
Hz, 3H), 3.54, (s, 3H), 4.20 (m, 1H), 4.52 (m, 1H), 7.10–7.5 (series of m, Ar, 11H). Anal. calcd for
C22H22NO2S3P: C, 57.50; H, 4.83; N, 3.05. Found: C, 57.82; H, 4.96; N, 2.92.
3.10. (−)-6,60-Bis(methoxy)[1,10-biphenyl]-2,20-diyl-O,O0-bis[5-methyl-2-(1-methylethyl)-cyclohexyl]-
carbothioic ester 17
A solution of racemic dimercaptan 1 (0.95 g, 3.4 mmol) and Et3N (2.4 mL, 17.3 mmol) in dry benzene
or toluene (20 mL) was added to a solution of (1R,2S,5R)-(−)-menthyl chloroformate (1.78 g, 8.16
mmol) at rt. After 1 h of stirring, the crude reaction was washed with a 10% HCl solution. The organic
phase was washed with H2O (100 mL), dried over Na2SO4 and evaporated to give a 1:1 diastereomeric
mixture of 1. Each diastereomer was separated by flash chromatography using a 2:3 mixture of petroleum
20
ether:CH2Cl2 as eluent (1.97 g, 90%). One diastereomer, first eluted: 98% de, mp 120–122°C; [α]D
−0.6 (c 1.1, CHCl3); 1H NMR δ 0.71 (d, J=7.2 Hz, 6H), 0.83 (d, J=7.2 Hz, 6H), 0.85 (d, J=7.2 Hz, 6H),
0.8–2.0 (series of m, 18H), 3.67 (s, 6H), 4.67 (m, 2H),), 6.97 (d, J=8.1 Hz, Ar, 2H), 7.29 (d, J=8.1 Hz, Ar,
2H), 7.37 (t, J=8.1 Hz, Ar, 2H); 13C NMR δ 16.28, 20.60, 21.87, 23.34, 26.02, 31.39, 33.98, 40.56, 46.90,
55.74, 77.86, 111.74, 128.09, 129.00, 129.34, 129.92, 157.24, 168.53. Anal. calcd for C36H50O6S2: C,
67.26; H, 7.84. Found: C, 67.12; H, 8.00.
3.11. (−)-6,60-Bis(methoxy)[1,10-biphenyl]-2,20-diyl-O,O0-bis[5-methyl-2-(1-methylethyl)-cyclohexyl]-
carbothioic ester 17
20
1
One diastereomer, second eluted: 93% de, mp 166–169°C; [α]D −62.4 (c 1, CHCl3); H NMR δ
0.70 (d, J=7.2 Hz, 6H), 0.81 (d, J=7.2 Hz, 6H), 0.84 (d, J=7.2 Hz, 6H), 0.8–2.1 (series of m, 18H), 3.68
(s, 6H), 4.65 (m, 2H), 7.00 (d, J=8.1 Hz, Ar, 2H), 7.22 (d, J=8.1 Hz, Ar, 2H), 7.40 (t, J=8.1 Hz, Ar, 2H);
13C NMR δ 16.41, 20.53, 21.89, 23.46, 26.07, 31.29, 33.97, 40.77, 46.95, 55.74, 77.99, 111.78, 128.10,
128.90, 129.45, 129.88, 157.19, 168.61. Anal. calcd for C36H50O6S2: C, 67.26; H, 7.84. Found: C, 67.16;
H, 8.04.
3.12. (+)-2,20-Dimercapto-6,60-dimethoxy-1,10-biphenyl 1
A solution of 17 (0.26 g, 0.40 mmol) in dry Et2O (40 mL) was added dropwise to a mixture of LiAlH4
(0.15 g, 4.0 mmol) in dry Et2O (40 mL) at rt. The reaction was stirred at this temperature for 24 h. A
5% HCl solution was added cautiously at 0°C and the organic phase extracted with Et2O (3×20 mL) and