Ring-closing enyne metathesis of terminal alkynes with propargylic hindrance.

The ring closing enyne metathesis of substrates with propargylic hindrance was investigated, revealing the successful combination of the Stewart-Grubbs catalysts and microwave heating sometimes up to 170 °C for oxacycles. Medium-sized rings were obtained from terminal alkynes previously reputed as reluctant substrates. This unmatched combination was applied to the synthesis of carbocycles and oxacycles. In addition, this is the first report on the use of the Stewart Grubbs catalyst in ring closing enyne metatheses.