The Pechmann Reaction and Regioselective Oxidation with Selenium Dioxide. Synthesis of the 12-Demethoxydefucogilvocarcin Ring System

Abstract

The Pechmann condensation of resorcinol with ethyl 2-oxocyclohexanecarboxylate and ethyl (2-oxocyclohexyl)acetate provided pyrone 3 (3-hydroxy-6-oxo-7,8,9,10-tetrahydro-6H-dibenzo[b,d]pyran) and seven-membered lactone 5 (3-hydroxy-6-oxo-6,7,8,9,10,11-hexahydrodibenz[b,d]oxepin), respectively. Condensation of 1,5-dihydroxynaphthalene with ethyl 2-oxocyclohexanecarboxylate followed by regioselective oxidation with selenium dioxide and dehydrogenation with Pd/C furnished the 12-demethoxydefucogilvocarcin ring system 12 (1,10-dimethoxy-6-oxo-6H-benzo[d]naphtho[1,2-b]pyran) in five steps and 38% over-all yield.