LIGAND-EXCHANGE REACTION OF SULFOXIDES IN ORGANIC-SYNTHESIS - A NOVELMETHOD FOR GENERATION OF MAGNESIUM ENOLATES AND ITS APPLICATION TO SYNTHESIS OF ALPHA-HALOCARBOXYLIC ACID-DERIVATIVES AND ALPHA-HALOALDEHYDES

A new method for synthesis of alpha-halo(Cl, F)carboxylic acid derivat ives and alpha-haloaldehydes is described. alpha-Halo-alpha-sulfinyl c arboxylic acid, esters, and alpha-Halo-alpha-sulfinyl aldehydes were e asily prepared from aryl 1-haloalkyl sulfoxides and alkyl chloroformat e and ethyl formate, respectively, in good yields. alpha-Chloro-alpha- sulfinyl amides were synthesized from (p-tolylthio)acetic acid. Ligand exchange reaction of the sulfinyl group of these acids, esters, amide s, and aldehydes with ethylmagnesium bromide gave the magnesium enolat es, which were treated with water to give alpha-halocarboxylic acid de rivatives and alpha-chloroaldehydes in good yields. The magnesium enol ates derived from the alpha-chloro-alpha-sulfinyl acid derivatives wer e trapped with carbonyl compounds to afford the adducts, which were tr ansformed to alpha, beta-epoxy carboxylic acid derivatives. Thermal el imination of the sulfinyl group in the alpha-halo-alpha-sulfinyl acid derivatives and the alpha-halo-alpha-sulfinyl aldehydes gave alpha-hal o-alpha, beta-unsaturated carboxylic acid derivatives and alpha-halo-a lpha, beta-unsaturated aldehydes in high yields.