A MEANS FOR STEREOCONTROLLED INTRODUCTION OF THE C-2 OXYGEN SUBSTITUENT IN FUNCTIONALIZED CIS-TRICYCLO[9.3.1.03,8]PENTADECANONES RELATED TO TAXOL

Several optically pure cis-tricyclo[9.3.1.0(3,8)]pentadecanones have been prepared via anionic oxy-Cope rearrangement of exo-norbornanol precursors that have been obtained by convergent coupling of two functionalized reaction partners. The sigmatropic rearrangement is shown to proceed with exceptionally good stereochemical transmission because of universal adherence to the same endo-chair transition state. The atropisomeric aspects of this pivotal transformation are addressed. Also investigated was the proclivity of the products to undergo transannular hemiketal formation following osmylation of the bridgehead double bond. As matters turn out, the operation or nonoperation of this intramolecular addition to the C-9 carbonyl group is amenable to control merely by adjusting properly the stereochemistry of a single pendant substituent.