Stereoselective Barbier-Type Allylations And Propargylations Mediated By Cpticl3

CpTiCl2, prepared in situ by manganese reduction of CpTiCl3, 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 Et3N center dot 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.