Two Distinct Cyclizations of 2-Propenyl-1-ethynyl Benzenes with Aryldiazo Esters Using Au and Rh/Au Catalysts Respectively

Abstract

This work reports the development of two catalytic cyclizations of 2-propenyl-1-ethynylbenzenes with aryldiazo esters. Cationic gold catalyst produces 2-substituted 3-alkenyl-1H-indenes with substrates over a reasonable scope. Our mechanistic study suggests that arydiazo esters attack at the cyclopropyl moieties of gold carbene intermediates, followed by skeletal rearrangement of resulting intermediates. In the presence of Rh2(esp)2 additive, the same gold catalyst alters the chemoselectivity of these reactants to afford tetrahydro-1H-cyclopropa[b]naphthalenes with excellent stereoselectivity. Herein, Rh(II) catalyst catalyzed the reactions of the same 1,6-enynes with diazo species to form cyclopropenes initially, and a cationic Au(I) catalyst allows their subsequent reactions with the tethered alkenes. Preferable E-selectivity and synergistic effects of Au/Rh catalysts are rationalized in a postulated mechanism.