Preparation of Some α-Substituted Cyclopropanecarboxylic Acids via Dichlorocarbene

Abstract

Some α, β-unsaturated esters (1), including trans-crotonate, trans-α-methoxycrotonate, irans-α-fluorocrotonate, trans-cinnamate, trans-α-chlorocinnamate, cis- and trans-α-fluorocinnamates, fumarate, and maleate, were allowed to react with dichlorocarbene, generated by the thermal decomposition of sodium trichloroacetate at 120-160°C, to give the corresponding β, β-dichlorocyclopropanecarboxylates (2) in fair to good yields (38-88%). The additions of dichlorocarbene to these esters were stereospecific. A similar reaction of n-butyl acrylate gave only a very low yield (6%) of the dichlorocarbene adduct, probably because of the accompanying polymerization of the starting ester. The reduction of 1-unsubstituted or 1-methoxysubstituted 2, 2-dichloro-3-methylcyclopropanecarboxylate with tri-n-butyltin hydride at 90°C yielded both the completely reduced (3) and the partially reduced esters (4 and 5). That of 1-fluoro-substituted ester gave only the completely reduced product. These cyclopropanecarboxylates (2 and 3) were hydrolyzed with potassium hydroxide to give the corresponding free acids (6 and 7) in good yields (72-92%). The properties (bp, mp, nᴅ, pmr spectral data, etc.) of the cyclopropanecarboxylic acids and esters thus prepared are described.