Metal alkoxides reactions with silyl esters

Functionally substituted benzylic, allylic, and vinylic compounds containing alkoxides, esters, ethers, nitriles, or amides can be reacted with halosilanes under Barbier conditions using HMPT to yield C- and O-silylated products, 1,2- or 1,4-addition products, as well as reductive dimers. Radical and anionic intermediates are postulated, based on SET reactions from the metal, and multiple silated species can be obtained. The use of the TMSCl-Mg-HMPT system has been extensively investigated by Galas group [85] at the University of Bordeaux, and their work has greatly advanced the science of the Barbier reaction with silanes. 

In addition to the general procedure iUusIrated by Eq. (2.182), another route has been employed for the synthesis of metal alkoxides (and particularly analogous siloxides) by the reaction of metal alkoxides with esters (and silyl esters) (Section 4.3). Further, the reactions of metal alkoxides with acyl halides (or hydrogen halides) and unsaturated substrates such as CO, CO2, CS2, organic-isocyanates and isothiocyanates, chloral, etc. have been utilized for the preparation of haUde-alkoxides (Section 4.11) and interesting insertion products (Section 4.12), respectively. 

As discussed already (Section 2.8), metal alkoxides undergo transesterification reactions with organic as well as silyl esters as illustrated by Eqs (2.201), (2.202), and (2.203) ... 

Stannyl enol ethers are prepared typically from the corresponding metal enolates and tin electrophiles. A convenient protocol is the reaction of enol carboxylate with tin alkoxide (Scheme 3-190). In contrast to silyl enol ethers, stannyl enol ethers usually exist as mixtures of C-Sn (ketone) and O-Sn (enol ether) forms. For example, acetone and carboxylate esters exist mostly as a C-Sn (ketone) form. In general, the 0-Sn (enol ether) tautomers are more nucleophilic to react with electrophiles faster than the C-Sn (ketone) tautomers. 

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