Indium-mediated alkynylation of Baylis–Hillman acetates: a novel route to 1,4-enynes

Baylis–Hillman acetates undergo smooth alkynylation with aryl-susbstituted iodoalkynes in the presence of indium metal in refluxing dichloromethane to furnish 1,4-enynes in high yields with (E)-stereoselectivity. In the absence of Lewis acid, the reaction follows both SN2 and SN2′ pathways affording 1:1 mixtures of 1,4-enynes. Upon addition of 10 mol % of InBr3, the reaction proceeds preferably in the SN2′ manner. In the case of adducts derived from acrylonitrile, the corresponding products are obtained in fairly good yields and with (Z)-stereoselectivity.