Titanacyclopropane intermediate

It is remarkable that even cyclobutylmagnesium bromides react cleanly with titanium alkoxides to yield reactive titanacyclopropane intermediates that reductively cyclopropa-nate N,N-dialkylformamides. This constitutes the first synthesis of the highly strained N,N-dialkylbicyclo[2.1.0]pent-5-ylamines (Table 11.9, entries 29—31). 

Ally) ethers are selectively cleaved with titanium(lV) isopropoxide and commercially available Grignard reagents like /i-butyl- or cyclohexylmagnesium chloride [Scheme 4.229].432 Neither benzylidene acetals nor more highly substituted allylic ethers suffer under the reaction conditions. A mechanism for the reaction implicates formation of the titanacyclopropane intermediate 229.1 as the first step. Ligand exchange with an unsubstituted allyl ether affords intermediate 229.2. -Elimination to the allyltitanium(lV) alkoxide 2293 followed by hydrolysis returns the deprotected alcohol. The reaction closely resembles an earlier method based on zirconium.433... 

Eisch, J. J., Adeosun, A. A., Gitua, J. N. Organic chemistry of subvalent transition metal complexes, 27. Mechanism of the kulinkovich cyclopropanol synthesis Transfer-epititanation of the alkene in generating the key titanacyclopropane intermediate. Eur. J. Org. Chem. 2003,4721-4727. 

If an alkene is present in the reaction mixture the intermediate, titanacyclopropane, undergoes facile ligand exchange, giving new titanium species, which react further in the catalytic cycle. Thus, various alkenes can be involved in this reaction, inter- or intramolecularly, allowing the preparation of numerous cyclopropane derivatives. In the presence of a chiral titanium alcoholate the reaction can be performed with good enantioselectivity (Scheme 110).319... 

Kulinkovich, O. G. Titanacyclopropanes as versatile intermediates for carbon-carbon bond formation in reactions with unsaturated compounds. PureAppi. Chem. 2000, 72,1715-1719. 

Titanacyclopropanes as versatile intermediates for carbon-carbon bond formation in reactions with unsaturated compounds 00PAC1715. 

Kulinkovich Cyclopropanation. The Kulinkovich method produced cyclopropanols from carboxylic acid esters and ethylmagnesium bromide in the presence of catal3d ic amount of titanium tetraisopropoxide (Scheme 4). The intermediate was proposed to involve titanacyclopropane. Generally, good to excellent yields were observed for 1-alkylcyclopropanols (55). 1,2-Disubstituted cyclo-... 

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