Titanacyclopropanes as versatile intermediates for carbon-carbon bond formation in reactions with unsaturated compounds

Dialkoxytitanacyclopropane intermediates [or titanium (II)-olefin complexes] generated in situ from ethylmagnesium bromide and titanium (IV) isopropoxide react with allylic alcohols and allylic ethers to afford S 2' allylic ethylation products. The reaction proceeds with high regioselectivity and with low to high -stereoselectivity. This observation and others suggest a reaction mechanism involving an EtMgBr-initiated formation of titanacyclopentane ate complex from titanacyclopropane-olefin complex as a key step. Based on this assumption, a modified mechanism of titanium-mediated cyclopropanation of esters with Grignard reagents is proposed.