Titanium tetraisopropoxide-magnesium

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) ...

Allyltitanium complexes (22) readily add to carbonyl compounds with high regio- and stereo-selection. They are prepared by reaction of a chlorotitanium complex (21) with an allyl-magnesium or -lithium derivative (equation 13). Some of these unsaturated Ti complexes, like (23)-(25) in Scheme 2, obtained from allylmagnesium halides or allyllithium by reaction with titanium tetraisopropoxide or titanium tetramides, are known as titanium ate complexes . The structure of these ate complexes, at least from a formal point of view, can be written with a pentacoordinate Ti atom. Some ate complexes have synthetic interest, as is the case of (allyl)Ti(OPr )4MgBr which shows sharply enhanced selectivity towards aldehydes in comparison with the simple (allyl)Ti(OPr )3. ... 

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.

Abbreviations. AITSB, aluminum tri-sec butoxide TTIP, titanium tetraisopropoxide TTE, titanium tetraethoxide EtjO, diethyl ether MgChe, magnesium chelate MgAc, magnesium acetate aq.surf, aqueous solution of surfactant. 

Terminal epoxides react slowly with sulfonyl carbanions such as the homoenolate equivalent (1) (eq 4). With disubstituted epoxides and cyclic epoxides the reactions are slower still. For example, reaction of the lithio derivative of ethyl phenyl sulfone with cyclopentene oxide occurs in excellent yield (98%) after 10 h reflux in toluene. It has been reported that, in some cases, the addition of a Lewis acid (magnesium bromide, boron trifluoride etherate, 4 titanium tetraisopropoxide, MeOAl(i-Bu)2 ) or HMPA iirproves the yield dramatically. 

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