Stereoselective Access to the Basic Skeleton of Tetracyclic Diterpenes via a Sequence of Consecutive , , and Cycloaddition Reactions

Article abstract of DOI:10.1021/jo00068a026

Benzocyclobutenes 9a, 9b, 23, and 24, prepared from 1,5-hexadiyne in good yields in a sequence involving <3 + 2> annelation and <2 + 2 + 2> cycloaddition reactions, underwent an intramolecular <4 + 2> reaction to afford the basic skeleton of tetracyclic diterpenes phyllocladane and kaurane.The factors governing the stereochemistry of the Diels-Alder reaction have been elucidated.A carbonyl group at C12 favored the kaurane stereochemistry (58:42) whereas acetal or silylether functions at that same position led to a highly (97:3) or totally stereoselective formation of the phyllocladane ring system.