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(+)-(M)-2,2’-Dibromo-6,6’-bis(methoxymethyl)biphenyl (M-41): Prepared following the
same protocol, starting from (+)-(M)-(6,6’-dibromobiphenyl-2,2’-diyl)dimethanol (39; 1.5 g,
4.0 mmol); colorless prisms; m.p. 86 - 88 °C; [ ] 20
α D = -37.3 (c = 1.0, ethanol); yield: 1.37 g
(86%).
4.3 Preparation of Biphenylbisphosphines
(-)-(P)-(6,6’-Dimethoxybiphenyl-2,2’-diyl)bis(diphenylphosphine) (42) [(-)-(P)-MeO-BIPHEP]:
Butyllithium (5.4 mmol) in hexane (3.5 mL) was added dropwise to a solution of (+)-(M)-
2,2’-dibromo-6,6’-dimethoxybiphenyl (35; 1.0 g, 2.7 mmol) in toluene (8.0 mL) and diethyl
ether (2.0 mL) at -75 °C. After 30 min, a solution of chlorodiphenylphosphine (1.1 mL, 1.3 g,
6.0 mmol) in toluene (10 mL) was added dropwise in order to keep the temperature below
-70 °C. The mixture was then warmed up to 25 °C and water (10 mL) was added. The phases
were separated and the aqueous one was extracted with ethyl acetate (2 × 10 mL) to give,
after evaporation of the volatiles, a colorless solid which was recrystallized from ethanol to
afford colorless needles; m.p. 213 - 215 °C (ref. [16] m.p. 214 - 215 °C); [ α ] D = -42.4 (c = 1.0,
[16]
chloroform), ee > 99% [ref. [ ] = -42.5 (c = 1.0, chloroform), ee 99.7%]; yield: 1.01 g
20
α
(64%).
D
(+)-(M)-(6,6’-Dimethoxybiphenyl-2,2’-diyl)bis(diphenylphosphine) (42) [(+)-(M)-MeO-BIPHEP]:
Prepared following the same protocol starting from (-)-(P)-2,2’-dibromo-6,6’-
dimethoxybiphenyl (35; 1.0 g, 2.7 mmol); colorless needles; m.p. 213 - 215 °C (ref. [16] m.p.
20
D
214 - 215 °C); [ α ] = +41.7 (c = 1.0, chloroform), ee > 98.5% [ref.
chloroform), ee 98.5%]; yield: 1.12 g (66%).
20
[16] 20 [ α ] D = +41.3 (c = 1.0,
(±)-(PM)-(6,6’-Diethoxybiphenyl-2,2’-diyl)bis(diphenylphosphine) (43): tert-Butyllithium (30
mmol) in pentane (21 mL) was added dropwise to a solution of (±)-(PM)-2,2’-dibromo-6,6’-
diethoxybiphenyl (36; 3.0 g, 7.5 mmol) in tetrahydrofuran (30 mL) at -75 °C. After 30 min, the
reaction mixture was treated with a solution of chlorodiphenylphosphine (3.5 mL, 4.2 g, 19 mmol)
in tetrahydrofuran (20 mL) and immediately allowed to reach 25 °C. The solvents were removed,
the residue was dissolved in dichloromethane (35 mL) and water (20 mL) was added. The usual
extraction procedure with dichloromethane (2 × 20 mL) afforded a white solid which was
recrystallized from ethyl acetate to afford colorless prisms; m.p. 253 - 254 °C; yield: 3.89 g (85%).