Phosphine → 2,2'-Dibromo-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthalene

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Reaction Steps

Of the starting optically active phosphine compounds L1, the optically active compound of formula (III), i.e., 2,2'-bis(diphenylphosphinyl)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (hereinafter abbreviated as OcH-BINAP) can be synthesized, for example, as follows. 2,2'-Dibromo-1,1'-binaphthyl synthesized by the process disclosed in H. Takaya, et al., J. Orc. Chem., Vol. 51, p. 629 (1986) is hydrogenated in the presence of a ruthenium-on-carbon catalyst to obtain 2,2'-dibromo-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (2,2'-dibromo-1,1'-bitetrahydronaphthalene), which is then reacted with metallic magnesium to form a Grignard reagent. The resulting Grignard reagent is condensed with diphenylphosphinyl chloride to synthesize racemic OcH-BINAP. The racemate is optically resolved by recrystallization from a mixed solvent of chloroform and ethyl acetate in the presence of optically active dibenzoyltartaric acid as a resolving agent, and the precipitated crystal collected by filtration is treated with 1N sodium hydroxide to obtain a phosphine oxide. The optical purity of the phosphine oxide is determined by high performance liquid chromatography using an optically active column, and the above recrystallization operation is repeated until the product becomes optically pure. The thus obtained optically active phosphine oxide is then reduced by using trichlorosilane to obtain optically active OcH-BINAP.

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