On the mechanism of titanium-catalyzed cyclopropanation of esters

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Key words: cyctopropanation, cyclopropanots, titanium alkoxides, Grignard reagents, esters. 13-elimination, titanacyctopropanes. The addition of monoalkylated ...

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Russian Chemical Bulletin, VoL 40, No. 2, FebrTmry', 2000

Brief Communications On the mechanism of titanium-catalyzed cyclopropanation of esters with aliphatic organomagnesium compounds. Deuterium distribution in the reaction products of (CD3)xCHMgBr with ethyl 3-chloropropionate in the presence of titanium tetraisopropoxide O. L. Epstein, A. L Savehenko, and O. G. Kulinkovich* Department of Organic Chemistry, Belorussian State Universi~', 4 prosp. F. Skorito,, 220050 Minsk, Belar~Ls. Fax: 3 75 (017) 226 4998. E-mail: kulinkovieh @chem. bsu. unibeL by The reaction of ICD3)_~CHMgBr with ethyt 3-chtoropropionate in the presence of catalytic amounts of Ti(OPr') 4 results in ( E)- I -~,2-chloroethyl)- 3,3-dideuterio-2-trideuteriomethylcyclopropanol and (CD3)2CDH, identified by mass spectrometry. The reaction mechanism is discussed. Key words: cyctopropanation, cyclopropanots, titanium alkoxides, Grignard reagents, esters. 13-elimination, titanacyctopropanes.

The addition of monoalkylated titanium derivatives to carbonyl compounds it characterized by high chemoand stereosclectivity, l Organotitanium compounds containing two and more alkyl residues are usually unstable and could not find use in organic synthesis ('or a long time. Tebbe and co-authors have first reported z the use of the Me2AICI-CH2TiCp2 complex, the product of interaction of 2 equivs, of M%AI with Cp2TiCI 2. as a reactant for homologization of alkenes and methylenation of ketones. As applied to esters, this reaction was described by Pine and c o - a u t h o r s ) Later. simplified procedures have been used 4,5 for the preparation o f titanium-methylene complexes, including thermolysis of easily accessibledimethyltitan0cenel 5 It is assumed that these complexes are formed from the corresponding dimethyltitanium derivatives by

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