The STOBBE condensation. X. The cyclisation of (E)‐3‐methoxycarbonyl‐4‐(5′‐methyl‐2′‐furyl)‐but‐3‐enoic acid, and (E)−3‐methoxycarbonyl‐4‐(2′‐furyl)‐pent‐3‐enoic acid, to Benzofuran Derivatives

Abstract

AbstractThe condensation of 5‐methyl‐furan‐2‐aldehyde and 2‐furyl‐methyl ketone with dimethyl succinate using either potassium t‐butoxide or sodium hydride as condensing agents, gives predominantly (E)‐3‐methoxycarbonyl‐4‐(5′‐methyl‐2′‐furyl)‐but‐3‐enoic acid 1a and (E)‐3‐methoxy‐carbonyl‐4‐(2′furyl)‐pent‐3‐enoic acid 5 respectively. Their configurations are inferred by cyclisation with sodium acetate in acetic anhydride to the corresponding benzofuran derivatives 2,6. Alcoholysis of (E)‐3‐carboxy‐4‐(5′‐methyl‐2′‐furyl)‐but‐3‐enoic anhydride 3 gives the half‐ester 1c which is isomeric with the half‐ester 1a. A competing side reaction also gives the self‐condensation product of the succinic ester 4.