Enantiospecific synthesis of the proposed structure of the antitubercular marine diterpenoid pseudopteroxazole: Revision of stereochemistry

An enantiospecific synthesis of structure 1, previously assigned to the ant itubercular marine natural product pseudopteroxazole, has been accomplished as outlined in Scheme 1. Coupling of diene acid 3 and amino phenol 4 produ ced the amide 5, which was subjected to a novel oxidative intramolecular Di els-Alder reaction to generate the tricyclic lactam 6a stereoselectively. T his product was transformed via intermediates 7-11 into the diene 13. Catio nic cyclization of 13 afforded two diastereomeric tricyclic amphilectanes w hich were separated and transformed by parallel four-step sequences into 1 and 2, respectively. Neither 1 nor 2 were identical with pseudopteroxazole, indicating a need for revision of the structure, probably to 16.