Studies toward the synthesis of menogaril: Synthesis of A-ring precursors and their conversion to the tetracyclic core via the benzannulation reaction

A model study for the synthesis of menogaril is reported which involves the benzannulation reaction of a Fischer carbene complex with an alkyne that c ontains the A-ring of the tetracyclic core of menogaril. The synthesis of m ethoxy and benzyloxy derivatives of this alkyne are reported as well as the reaction of the methoxy derivative with an o-methoxyphenyl carbene complex to generate a tricyclic naphthol containing three of the four rings of men ogaril core. Completion of the model study and the synthesis of the tetracy clic anthracyclinone core of menogaril was accomplished by an intramolecula r Friedel-Crafts cyclization.