Chlorotitanium triisopropoxide

The best titanium mediator appears to be methyltitanium triisopropoxide, yet good yields are also obtained with titanium tetraisopropoxide and chlorotitanium triisopropoxide. The methyl group on titanium serves as a dummy alkyl ligand which is eliminated as methane after hydride transfer from the... 

Table 11.4. 1,2-Disubstituted cyclopropanols 22 from carboxylic acid esters 8 and 2-substituted ethyl-magnesium halides in the presence of titanium tetraisopropoxide or chlorotitanium triisopropoxide. Entry Starting Product Conditions Yield Ref. Ester R1 R3 [mol% (%) R2 Ti(OR)4] (d. r. Z/Eb) ...

In subsequent investigations the generality of the above behavior was established for n-alkyltitanium compounds 21,22 77,78). For example, quenching ethyllithium 25 with chlorotitanium triisopropoxide 3 affords 9, which reacts in situ with a 1 1 mixture of 19 and 20 to afford essentially only the aldehyde adduct 23 (Equation 9) 77). 25 itself reacts at 0 °C almost statistically ... 

If carbanions are to be titanated, alkoxy or amino ligands at titanium are most likely to ensure success. Sulfur or phosphorus ligands have not been tested. In rare cases electrontransfer instead of titanation sets in, forming Ti(III) species which are generally unsuitable for useful chemistry. This is most likely to occur if the carbanion is very electron rich, e.g., in case of dianions or extended anionic K-systems. We have noticed that this undesired property decreases in going from chloro to alkoxy and finally to amino ligands at titanium. For example, dianions derived from carboxylic acids reduce chlorotitanium triisopropoxide 3 to some extent, whereas quantitative double titanation occurs with chloro- or bromotitanium tris(diethylamide) 15 77>. Addition of amines to the reaction mixture has similar effects 77). 

Consequently, various Grignard reagents have been shown to be effective for the intramolecular cyclopropanation reactions with insignificant differences in yields. Whereas several titanium alkoxides and aryloxides can also be employed, chlorotitanium triisopropoxide and methyltitanium triisopropoxide have often been found to be the titanium reagent of choice. Ether, THE, toluene, or even dichloromethane are generally appropriate reaction solvents. 

Table 11.4. 1,2-Disubstituted cyclopropanols 22 from carboxylic acid esters 8 and 2-substituted ethyl-magnesium halides in the presence of titanium tetraisopropoxide or chlorotitanium triisopropoxide.

Carbon disulfide s. under BuLi Methyl iodide s. under Co iCO) and CoClj 2,3-Dichloro-5,6-dicyanoquinone s. under RLi Iminocarbonyl chlorides s. under Mg Trimethylsilyl chloride s. under Zn Chlorotitanium triisopropoxide s. under BuLi... 

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