O-Silylated steroidal cis-aminoalcohols as chiral auxiliaries: highly diastereoselective Pd-catalyzed cyclopropanation of α,β-unsaturated aldimines

α,β-Unsaturated imines, obtained from cis-17-silyloxy-16-amino steroids and α,β-unsaturated aldehydes, react with diazomethane in the presence of a catalytic amount of Pd(OAc)2 with high chemo- and diastereoselectivities to form steroidal cyclopropanocarbaldimines; chromatography on silica gel gives the substituted cyclopropanocarbaldehydes with a high enantiomeric excess and allows recovery of the chiral steroidal auxiliaries.