Titanium Tetraisopropoxide transesterification

Other esters of 2-chloro-2-cyclopropylideneacetic acid can easily be prepared from the methyl esters 1-Me, 2-Me by transesterification with the appropriate alcohol component under titanium tetraisopropoxide catalysis [20], as has been demonstrated for a number of benzyl and ethyl esters (Scheme 4) [9,10,21,22a]. 

Tamura et al. (170-172) discovered that, when reactions of ester-substituted nitrones with allylic alcohols are performed in the presence of an equimolar amount of titanium tetraisopropoxide under heating or at room temperature, transesterification takes place to form new nitrones bearing an inner alkene dipolarophile. The resulting nitrone substrates undergo regio- and stereoselective intramolecular cycloaddition reactions to give the ring-fused isoxazolidines (Scheme 11.52). This tandem transesterification/[3 + 2]-cycloaddition method leads to the selective... 

Enantiomerically pure carboxylic acids are routinely obtained from N-acylsultams by Hydrogen Peroxide assisted saponification with Lithium Hydroxide in aqueous THF. 4 Alternatively, transesterification can be effected under neutral conditions in allyl alcohol containing Titanium Tetraisopropoxide, giving the corresponding allyl esters which can be isomerized/hydrolyzed with Wilkinson s catalyst (Chlorotris(triphenylphosphine)rhodium(I)) in Et0H-H20. This provides a convenient route to carboxylic acids containing base-sensitive functionality. Primary alcohols are obtained by treatment with L-Selectride (Lithium Tri-s-butylborohydride) in THF at ambient temperature. ... 

Transesterification of methyl esters to 2-(trimethylsilyl)ethyl esters under mild and neutral conditions takes place in the presence of titanium tetraisopropoxide (eqs 6-8). Deprotection of the 2-(trimethylsilyl)ethyl ester in the presence of an O-TBDMS protected secondary hydroxyl group has been achieved (eq Q). An alternative method for the transesterification uses l,8-diazabicyclo[5.4.0]undec-7-ene/lithium bromide and 2-(trimethylsilyl) ethanol. ... 

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