Synthesis of 3(2H)-Furanones by the Iron Carbonyl-promoted Cyclocoupling Reaction of α,α′-Dibromo Ketones and Carboxamides. A Convenient Route to Muscarines

Abstract

Abstract Reaction of α,α′-dibromo ketones and N,N-dimethylcarboxamides with the aid of Fe2(CO)9 affords the corresponding reductive cyclocoupling products, 5-(dimethylamino)tetrahydro-3-furanones. In usual, the adducts derived from di-s-alkyl ketone dibromides easily eliminated dimethylamine to afford 3(2H)-furanones. N,N-Dimethylformamide (DMF), N,N-dimethylacetamide, N,N-dimethylbenzamide, and N-methylpyrrolidone have been used as dibromo ketone receptors. Thus, this general method provides a new, singleflask procedure for the preparation of the oxygen-containing five-membered ketones. The iron carbonyl-promoted 3+2 cyclocoupling reaction is interpreted as proceeding via a stepwise cycloaddition of a reactive 2-oxyallyl–Fe(II) intermediate and carboxamide. A facile conversion of such furanones to muscarine alkaloids is described.