Titanacyclopropanes as versatile intermediates for carbon-carbon
bond formation in reactions with unsaturated compounds*
O. G. Kulinkovich
Department of Chemistry, Belarussian State University,
Fr. Skaryny av., 4, Minsk, 220080, Belarus
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.
*Lecture presented at the 13th International
Conference on Organic Synthesis (ICOS-13), Warsaw, Poland, 1-5 July
2000.
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