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A one-pot preparation of 2,5-dihydrothiophene-1,1-dioxide-3carboxylic acid (3-sulfolene-3-carboxylic acid) is reported. The carboxylation of 3-sulfolene, exclusively at the 3-position, using CO 2 and DBU proceeds to >90% conversion. A rapid workup gives 3-sulfolene-3-carboxylic acid, a stable precursor to 1,3-butadiene-2-carboxylic acid. High conversions to Diels-Alder adducts were obtained upon treatment of 3-sulfolene-3-carboxylic acid with various dienophiles.

The One-Pot Synthesis and Diels-Alder Reactivity of 2,5-Dihydrothiophene--1,1-dioxide-3-carboxylic Acid. -The title compound (III), which is a stable precursor of 1,3-butandiene-2-carboxylic acid, is synthesized and its reactivity towards various dienophils is tested. -(ANDRADE, G. S.; BERKNER, J. E.; LIOTTA, C. L.; ECKERT, C.; SCHIRALDI, D. A.; ANDERSEN, A.; COLLARD*, D. M.; Synth.