[2+2] Cycloaddition of Benzyne and Ketene Silyl Acetal as an Efficient Route to Benzocyclobutenones

Abstract

New and efficient synthetic approach to benzocyclobutene derivatives is described. Halogen-lithium exchange of ortho-halo aryl triflates (THF, -78°C) quickly generates arynes which react with the coexisting ketene silyl acetals to give [2+2] cycloadducts in high yields. The polarization of the aryne species induced by an adjacent alkoxyl group (inductively electron withdrawing) directs the regioselectivity of the cycloadditions. Subsequent acetal cleavage under acidic conditions gives various benzocyclobutenones in high yields.