Gold(i)-catalysed high-yielding synthesis of indenes by direct Csp3-H bond activation

A catalytic, practical and high-yielding procedure for the synthesis of indenes by direct C-sp(3)-H activation under gold(i) catalysis was developed. The scope of the protocol was determined by synthesizing some electron-neutral, electron-poor as well as electron-rich derivatives including the dibenzofurane and carbazole heterocycles. The mechanism of this reaction was elucidated by theoretical calculations using a ONIOM(M08-HX/mixed-basis:PM6) hybrid scheme. Thereby we found a pericyclic transformation involving a [1,5]-H shift generating a gold(i)-carbene that evolves to the indene derivative. In comparison with several reports, our protocol presents a direct activation of the C-sp(3)-H bond.