Synthesis of some thiophenium bis(t-butoxycarbonyl)methylides

Abstract

Thiophene derivatives react with di-t-butyl diazomalonate in the presence of rhodium(II) carboxylates to yield thiophenium bis(t-butoxycarbonyl)methylides. Rhodium(II) hexanoate is a more efficient catalyst than rhodium(II) acetate, shortening reaction times and increasing yields of the ylides. Series of 2-halogeno-, 2-alkyl-, 2-benzyl-5-halogeno-, and 2-benzyl-5-alkyl-thiophenium ylides are described. Whilst 2-methyl-, 2-ethyl-, and 2-isopropyl-thiophenes readily form the ylides in good yield, 2-t-butylthiophene appears to undergo further reaction to yield 1,3-bis-t-butoxycarbonyl-2-(3-t-butyl-6,6-bis-t-butoxycarbonyl-2-thioniabicyclo[3.1.0] hex-3-en-2-yl)methanide (2) whose structure has been confirmed by X-ray crystallography.