CLAISEN REARRANGEMENT OF THE LITHIUM ENOLATE OF 1-(2-THIENYL)ALKYL ALKANOATE AND THE BIRCH REDUCTION OF THE RESULTING 2-(3-THIENYL)ALKANOIC ACID.

Article abstract of DOI:10.1246/bcsj.56.1665

It was found that the Claisen rearrangement of the lithium enolate of 1-(2-thienyl)alkyl alkanoate in refluxing THF resulted in the formation of 2-(3-thienyl)alkanoic acid (2). Similarly, when the lithium enolate of 4-(2-thienyl)-4-butanolide was stirred at room temperature in the presence of hexamethylphosphoric triamide, 5,6-dihydro-4H-cyclopenta left bracket b right bracket thiophene-4-carboxylic acid was obtained. Further, it was found that the Birch reduction of 2 and subsequent alkylation with benzyl bromide gave a regioselective ring-opening product, 4-benzylthio-3-ethyl-3-alkanoic acid, in a good yield. The Birch reduction of 2-thienylacetic acid, followed by alkylation with benzyl bromide, also gave (Z)-3-benzylthio-3-hexenoic acid as the main product.