Phosphine-directed stereo- & regioselective Ni-catalyzed reactions of Grignard reagents with allylic ethers

摘要

Studies on the directed regio- and stereoselective M-catalyzed allylic substitution reactions involving methyl- and phenylmagnesium bromides and various acyclic and cyclic allylic ethers are reported. In the presence of a properly positioned internal Lewis base, C-C bonds can be formed catalytically and with excellent levels of selectivity. Internal chelation allows Ni-catalyzed C-C bond forming reactions that are otherwise non-selective, sluggish, or do not occur at all, to proceed to completion readily, in excellent yields, at ambient temperature and with high regio-and stereocontrol. Directed alkene isomerization highlights an especially attractive feature of the metal-catalyzed alkylation strategy: because the initial product contains a prostereogenic site that remains within reach of the internal Lewis base, it can be subjected to additional directed stereoselective manipulations. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 48]