Palladium-Catalyzed Cascade 5-endo-dig Cyclization of Ynamides to Form 4-Alkynyloxazolones
Tales A C Goulart1, Davi Fernando Back2, Sidnei Moura E Silva3
1Laboratório de Síntese, Reatividade, Avaliação Farmacológica e Toxicológica de Organocalcogênios CCNE, UFSM, Santa Maria, Rio Grande do Sul 97105-900, Brazil.
Abstract:
The selective synthesis of 4-alkynyloxazolones and their further applications as substrates to electrophile-promoted nucleophilic cyclization have been developed. The reaction of ynamides with terminal alkynes proceeded smoothly to give 4-alkynyloxazolones in the presence of a catalytic amount of palladium(II) acetate. The products were obtained with the sequential formation of new C-C and C-O bonds via a cascade procedure. The first step involved a carbon-oxygen bond formation, via a 5-endo-dig closure, which was confirmed by X-ray analyses of the crystalline sample. Subsequently, the reaction of 4-alkynyloxazolones with an electrophilic selenium source gave 3-phenylselanyl benzofuran derivatives via an electrophile-promoted nucleophilic cyclization.
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