Palladium-Catalyzed Cascade 5-endo-dig Cyclization of Ynamides to Form 4-Alkynyloxazolones

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.

Automated summary

The selective synthesis of 4-alkynyloxazolones and their application as substrates for electrophile-promoted nucleophilic cyclization were developed. The reaction of ynamides with terminal alkynes in the presence of a palladium(II) acetate catalyst resulted in the smooth formation of 4-alkynyloxazolones. The products were obtained through a cascade reaction involving the formation of new C-C and C-O bonds. The 4-alkynyloxazolones further reacted with an electrophilic selenium source to yield 3-phenylselanyl benzofuran derivatives through electrophile-promoted nucleophilic cyclization.