The utility of vinyl ethers and vinyl esters in the Khand reaction. The value of vinyl esters as ethylene equivalents and a modified synthesis of (+)-taylorione as an example

Abstract

The behaviour of various oxygenated alkenes in the Khand cyclisation reaction has been studied. Although several vinyl ethers reacted to give the expected oxygenated cyclopentenone products, usually with good levels of regioselectivity, the use of vinyl esters was found to afford, as the major products, reduced cyclopentenones in which the carbon–oxygen bond had been cleaved. This unexpected reaction was developed into an alternative procedure to using ethylene gas in the Khand reaction and was found to be applicable with a variety of alkyne substrates. The method was then extended to form the key step in the synthesis of the natural product (+)- taylorione (and (+)- nortaylorione).