Dimerization of Cyclopropanecarboxylic Acid Dianion and Thermal Decarboxylative Rearrangement of the Dimer to 2-Cyclopropyl-4,5-dihydrofuran

Article abstract of DOI:10.1021/jo00163a007

The dianion of cyclopropanecarboxylic acid (2) reacted with alkyl halides and deuterated water at temperatures below 0 deg C; however, self-condensation to the β-keto acid 3 was the only observed product at elevated temperatures.This observation contrasts the self-condensation of the ethyl ester where a trimeric diester alcohol is the product.Attempted mixed condensations of the dianion 2 and carboxylic acids without acidic α-protons did not proceed as well, 3 being the major product.Thermal decarboxylation of 3 did not yield the expected dicyclopropyl ketone; rather , a facile rearrangement in a sealed tube at 120 deg C occured, giving rise to 2-cyclopropyl-4,5-dihydrofuran.This "vinyl-cyclopropyl" type rearrangement does not occur through dicyclopropyl ketone or its enolate.