The STOBBE Condensation, Part IX. The cyclisation of (E)‐3‐Methoxycarbonyl‐4‐(5′‐methyl‐2′‐thienyl)‐but‐3‐enoic acid, and α,β‐bis‐(5‐methyl thenylidene)‐succinic anhydride, to benzothiophen derivatives

Publisher Website
Google Scholar
Abstract
The condensation of 5‐methyl‐thiophen‐2‐aldehyde with dimethyl succinate in the presence of potassium t‐butoxide or sodium hydride gave predominantly (E)‐3‐methoxy‐carbonyl‐4‐(5′‐methyl‐2′‐thienyl)‐but‐3‐enoic acid 1a, whose configuration is proved by cyclisation with sodium acetate in acetic anhydride to the corresponding benzothiophen derivatives 2. Alcoholysis of the derived (E)‐carboxy‐4‐(5′‐methyl‐2′‐thienyl)‐but‐3‐enoic anhydride 3 gives the half‐ester 1c which is isomeric with the half‐ester 1a. Condensation also gave the α,β‐bis‐(5‐methyl thenylidene)‐succinic acid 4a in small amounts. The derived anhydride 5 yields on pyrolysis 4‐(5′methyl‐2′‐thienyl)‐2‐methyl‐benzothiophen‐5,6‐dicarboxylic anhydride 6.

This publication has 2 references indexed in Scilit: