The stereoselective synthesis of rac-chokols A and G precursors described herein proceeds from the readily available gem-borazirconocene 2 by conjugate addition to 2-methylcyclopentenone to give the common intermediate 3, which is then transformed in a series of reactions to provide the chokols in overall yields of 16 and 17% respectively. Copyright (C) 1996 Elsevier Science Ltd.