Transannular Diels–Alder cyclization of a substituted 13-membered macrocyclic triene. An approach to the A.B.C.[6.6.5] rings of the Veratrum alkaloids

Abstract

The synthesis and Diels–Alder cyclization of a substituted macrocyclic 13-membered triene 45 is described. Tricyclic compound A.B.C.[6.6.5] 46 having ring junctions of cis-anti-cis (CAC) stereochemistry was used to investigate the possibility of introducing a hemiketal oxygen bridge between positions 9 and 4 of the Veratrum alkaloid skeleton.