Stereoselective Barbier-Type Allylations and Propargylations Mediated by CpTiCl.

CpTiCl, prepared in situ by manganese reduction of CpTiCl, is an excellent new system for the Barbier-type allylation and propargylation of carbonyl compounds. It can be used in catalytic amounts when combined with EtN·HBr/TMSBr, which acts as a regenerating system. The high regio- and stereoselectivity shown by this system makes it useful for prenylation and crotylation processes in the synthesis of natural products.