Development of new synthetic methods with aryl 1-chlorovinyl sulfoxides.

Abstract

Aryl 1-chlorovinyl sulfoxides were easily synthesized from ketones and aldehydes with aryl chloromethyl sulfoxide in three-steps with high overall yields. Low-temperature treatment of the aryl 1-chlorovinyl sulfoxides with alkyllithium or a Grignard reagent gave alkylidene carbenoids via a sulfoxide-metal exchange reaction. From the alkylidene carbenoids, acetylenic compounds, tetra-substituted olefins, and allenes were synthesized. Enolization of alpha-chloro alpha-sulfinyl ketones, which were synthesized from methyl esters and chloromethyl phenyl sulfoxide, is another method for the generation of aryl 1-chloroalkyl sulfoxides. Treatment of 1-chlorovinyl phenyl sulfoxides so generated with t-BuLi followed by some nucleophiles having an acidic hydrogen gave one-carbon elongated carboxylic acids and their derivatives. Conjugate addition of some carbanions with 1-chlorovinyl p-tolyl sulfoxides was found to have taken place. For example, reaction of 1-chlorovinyl p-tolyl sulfoxides with cyanomethyllithium gave high yields of cyclic enaminonitriles. Acidic treatment of the enaminonitriles afforded good yields of 4,4-disubstituted 2-cyclopentenones. By using unsymmetrical ketones and optically pure chloromethyl p-tolyl sulfoxide, this procedure suggests a good method for an asymmetric synthesis of optically pure 4,4-disubstituted 2-cyclopentenones. This method achieved an asymmetric total synthesis of (+)-alpha-cuparenone starting from methyl 4-methylphenyl ketone and (R)-(-)-chloromethyl p-tolyl sulfoxide. A novel synthesis of 2,4,4-trisubstituted 2-cyclopentenones is also successful using cyanomethyllithium and its homologues. Conjugate addition of the lithium enolate of tert-butyl acetate and its homologues gave high yields of the adduct, 3,3-disubstituted esters. Synthesis of various kinds of carboxylic acids and their derivatives and lactones was realized from the adducts.