(TRIALKYLSILYL)VINYLKETENES - SYNTHESIS AND APPLICATION AS DIENE COMPONENTS IN DIELS-ALDER CYCLOADDITIONS

New strategies for the synthesis of (trialkylsilyl)vinylketenes (''TAS -vinylketenes'') are described based on the photochemical Wolff rearra ngement of alpha-silyl-alpha'-diazo-alpha,beta-unsaturated ketones and the 4 pi electrocyclic ring opening of cyclobutenones. These remarkab ly robust vinylketenes undergo highly regioselective [4 + 2] cycloaddi tions with reactive olefinic and acetylenic dienophiles to produce hig hly substituted cyclohexenones and phenols in which the ketene carbony l dominates in controlling the regiochemical course of the reaction. T he stereochemical course of these cycloadditions follows the Alder end o rule, as illustrated in the reaction of nitropropene with TBS-vinylk etene 22.