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

Abstract

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 SN2′ allylic ethylation products. The reaction proceeds with high regioselectivity and with low to high trans-/cis-stereoselectivity. This observation and others suggest a reaction mechanism involving an EtMgBr-initiated formation of titanacyclopentane ate complex 10 from titanacyclopropane-olefin complex 7 as a key step. Based on this assumption, a modified mechanism of titanium-mediated cyclopropanation of esters with Grignard reagents is proposed.