Hydroxyl-directed intermolecular ketone-olefin couplings promoted by SmI2

SmI2-promoted intermolecular ketone-olefin couplings are facilitated and st ereocontrolled by hydroxyl groups incorporated within the starting material s. For example, the SmI2-induced ketone - olefin coupling reactions of alph a-hydroxy ketone 5 with ethyl acrylate, acrylonitrile, ethyl crotonate, and 2(5 H)-furanone proceeded with high stereocontrol to afford the syn-1,2-di ol products 6-9 in good yields. Excellent diastereoselectivity was achieved in the reductive couplings of beta-hydroxy aldehyde 21 and erythro-beta-hy droxy ketone 24 with acrylonitrile using SmI2, to produce the anti-1,3-diol s 22 and 25 in good yields. The sense of the stereo-selectivity was in full accord with a chelation-control model. In the proposed model, the stereoch emistry of the reaction product is explained by assuming that a cyclic kety l radical is generated during the initial single-electron reduction by SmI2 . This radical species results from the chelation of the Sm-III cation, att ached to the ketyl radical, with the hydroxyl group.