The addition of neomenthylphenylphosphine to (C6H5)2PCH=CH2 in boiling tetrahydrofuran catalyzed by potassium tert-butoxide gives the di(tertiary phosphine) (Nmen)(C6H5)PCH2CH2P(C 6H5)2 (I, Nmen = neomenthyl), which could be separated by fractional crystallization into pure diastereomers differing only in the configuration at the chiral phosphorus atom. Novel features in this new di(tertiary phosphine) are the chiral terminal neomenthyl group and the nonequivalent phosphorus atoms. Asymmetric homogeneous hydrogenations of the prochiral α-(acylamido)cinnamic acid derivatives C6H5CH=C(NHCOR)(CO2R′) (R = CH3, R′ = H and CH3; R = C6H5, R′ = H and C2H5) result in significant differences in optical yield behavior when rhodium(I) complexes of each of the two diastereomers of (Nmen)(C6H5)PCH2CH2P(C 6H5)2 are used. In particular, the optical yield range for the above four prochiral α-(acylamido)cinnamic acid derivatives is 31-85% for one of the diastereomers of I but only 42-56% for the other diastereomer. The related polyphosphorus compounds C6H5P[CH2CH2P(Nmen)(C 6H5)]2 and (Nmen)(C6H5)PCH2CH2P(S)(CH 3)2 have been obtained as mixtures of diastereomers from the additions of neomenthylphenylphosphine to C6H5P(CH=CH2)2 and CH2=CHP(S)(CH3)2, respectively, in boiling tetrahydrofuran catalyzed by potassium tert-butoxide.
ASJC Scopus subject areas
- Organic Chemistry