Stereocontrolled synthesis of acyclic terpenoids viaN-ylide [2,3]rearrangement of ammonium salts with the stereodefined isoprene unit

Abstract

Stereocontrolled elongation of a functionalized isoprene unit on the E or Z terminal methyl of terpenoids was achieved by N-ylide rearrangement of the common ammonium salts under selected reaction conditions. A 1,5-diene or conjugated triene skeleton can be furnished by reductive or oxidative removal of the amino group of the rearrangement product, respectively. As an application to natural-product synthesis, all-(E)-terpenoid (E)-11d and (E,Z)-terpenoid (Z)-11c were converted into β-sinensal and (13Z)-retinol, respectively. General aspects of these transformations and a plausible transition state for the N-ylide rearrangement are discussed.