Synthetic studies on the starfish alkaloid imbricatine. Construction of anent-imbricatine framework

A chiral synthetic route to the amino esters 5 and 6, which contain the fun damental framework of ent-imbricatine (ent-3), has been developed as a prel ude to the total synthesis of the starfish alkaloid imbricatine (3). The ro ute started from the sulfur-containing L-phenylalanine derivative 7 and pro ceeded through key steps such as cyclization of the amide 8 without racemiz ation, reduction to the 1,3-cis-tetrahydroisoquinoline 9, and introduction of a chiral alpha-amino acid moiety into the chloride 18 by the "bis-lactim ether" method.