Mechanistic study of the thermal decarboxylation and rearrangement of beta-keto-carboxylic acids to form 2,3-dihydrofurans

1-(cyclopropylcarbonyl)-cyclopropanecarboxylic acid has been shown to undergo thermal decarboxylation to form 5-cyclopropyl-2,3-dihydrofuran. The mechanism for this rearrangement was theorized to involve the opening of the cyclopropane ring to a vinyl group. The open ring would then react with the beta-keto carbonyl during a concerted decarboxylation via a pericyclic ring forming reaction to yield the dihydrofuran product. To test the likelihood of the vinyl intermediate a series of cyclopropane compounds and their vinyl analogs were proposed which would show if the vinyl system would also decarboxylate to the dihydrofuran. The beta-keto acids were formed by the reaction of the dianion of cyclopropane carboxylic acid and various acid chlorides. The vinyl compounds were formed by the reaction of the dianion of crotonic acid and the same acid chlorides as were used in the cyclopropane reaction. All compounds would be sealed in glass ampules under vacuum and heated to 120 °C in order to decarboxylate them. Electron donating and electron withdrawing substituents would be used in order to investigate their impact on the nature of the reaction. The rate of reaction was investigated both by NMR and also by GC analysis. Other potential reaction pathways were also investigated with model compounds being synthesized and ruled out due to their lack of rearrangement to the dihydrofuran compound.