Copper-catalyzed reaction of alpha-aryldiazoesters with terminal alkynes: a formal [3 + 2] cycloaddition route leading to indene derivatives

J Am Chem Soc. 2008 Dec 24;130(51):17268-9. doi: 10.1021/ja808080h.

Abstract

It was discovered that Cu(IPr)Cl-catalyzed reaction of terminal alkynes with alpha-aryldiazoacetates provides indene derivatives, formal [3 + 2] cycloaddition adducts. Excellent regio- and chemoselectivity were observed to afford either 3H- or 1H-indene esters depending on the reaction conditions employed. The reaction is proposed to proceed via tandem processes: alkyne insertion into copper-carbenoid, intramolecular electrophilic attack on the aromatic ring, and then isomerization.