Synthesis of A B C-ring subunit of C-nor-D-homo-steroidal alkaloids:towards the total synthesis of cyclopamine

A practical approach to the synthesis of the A,B and C-ring subunit of cyclopamine has been developed.This synthetic tactic highlights the utility of mandelate acetal-mediated resolution of the fused ring ketone(±)-4 and IBX-mediated oxidation cascades from 12 to 9.The availability of advanced intermediates from enantiomerically pure(+)-4 and 2 could provide efficient access to biologically active and structurally diverse C-nor-D-homo-steroidal alkaloids such as cyclopamine.