Stereoselective alkylation of [2-(diphenylphosphino)ferrocenyl]acetonitrile

Deprotonation of racemic [2-(diphenylphosphino)ferrocenyl]acetonitrile (1) with NaN(SiMe3)2 in THF followed by reaction with electrophiles MeI and Ph2PCl affords the substituted nitriles, 2-[2-(diphenylphosphino)ferrocenyl]propionitrile (2a) and 2-(diphenylphosphino)-[2-(diphenylphosphino)ferrocenyl]acetonitrile (2b), respectively. Whereas the former reaction yields a 15:1 mixture of isomers differing in configuration at the alkylated α-carbon from which the major diastereoisomer can be isolated by simple recrystallization, the latter gives 2b as a single diastereoisomer. The dominating product of the methylation reaction was characterized by X-ray diffraction analysis as (S,Rp/R,Sp)-2a, which is in accordance with the possible access of the electrophile towards deprotonated 1.