Palladium-catalyzed regioselective silaboration of 1,2-dienes

Palladium complexes catalyzed regioselective addition of the Si-B bond of ( dimethylphenylsilyl)pinacolborane to allenes in good yields. In the silabor ation of terminal allenes having electron-donating substituents such as alk yl and methoxy groups, the Si-B bond added to the internal C=C bond with re gioselective B-C and Si-C bond formation at the central and substituted car bon atoms of the allene, respectively. In contrast, the silylborane prefera bly added to the terminal C=C bond with exclusive Si-C bond formation at th e terminal carbon atom in the silaboration of allenes bearing electron-with drawing groups such as perfluoroalkyl group. 1,3-Disubstituted allenes also underwent the silaboration in good yields with varying regio- as well as s tereoselectivity. The silyl and boryl groups of the 2-borylallylsilanes thu s prepared were selectively utilized for further synthetic elaboration. Pal ladium-catalyzed coupling of the 2-borylallylsilanes with aryl iodides affo rded the corresponding 2-arylallylsilanes in fair-to-good yields. 2-Boryl-p i-allylpalladium complexes were successfully prepared by the reaction of th e 2-borylallylsilanes with PdCl2(CH3CN)(2). (C) 2000 Elsevier Science S.A. All rights reserved.