A HIGHLY EFFICIENT SYNTHESIS OF 3-METHYLCHOLANTHRENE

A five-step synthesis of 3-methylcholanthrene (1) has been achieved st arting from 5-methylhomophthalic anhydride and N,N-diethyl-1-naphthami de in 55% over all yield. Treatment of a solution of the preformed lit hium enolate of 5-methylhomophthalic anhydride (3) with an equimolar s olution of 2-lithio-1-naphthamide (4), followed by acid hydrolysis, pr ovides cleanly the spirobislactone 5 in 80% overall yield. In addition , the synthesis features a unique, highly selective double Friedel-Cra fts cyclization of the aryl diacid 2 with PPA to give rise, after acet ylation, to keto acetate 6.