A nickel-catalyzed carbozincation of aryl-substituted alkynes

The addition of dialkylzincs or diphenylzinc to substituted phenylacetylenes in the presence of catalytic amounts of Ni(acac)(2) in THF : NMP mixtures produces syn-carbozincation products with good to excellent regio-and stereoselectivity. After quenching with an electrophile (iodine, acyl chloride, allyl bromide) tetrasubstituted olefines are obtained in good to satisfactory yields. An intramolecular version of the reaction is possible using a terminal triple bond bearing an iodine at a remote position. More substituted iodo-alkynes furnish only reductive elimination products. An application to a stereoselective synthesis of (Z)-tamoxifen (Z: E > 99: 1) has been developed. (C) 1998 Elsevier Science Ltd. All rights reserved.