Transmetalation Brook rearrangement

Scheme 4.26 Precedent for Brook rearrangement/transmetallation of vinylsilanes bearing allylic alcohols...

Allenyl trialkylsilyl ethers 771 can be a-deprotonated with f-BuLi in THF at — 78 °C to give the allenyllithiums 77210901091. They underwent reverse Brook rearrangement to afford the silaacrolein enolates 773, which react with aldehydes and ketones to yield the a,/9-unsaturated acyl silanes 774 (Scheme 200). For enolizable aldehydes transmetallation with ZnCl2-TMEDA, and MgBr2 for ketones, provided better yields. 

Marek and co-workers found that magnesium-to-zinc transmetalation of the alkoxides derived from addition of acetylenic Grignard reagents to acyl silanes promoted the 1,2-Brook rearrangement. The resulting propargyl zinc intermediates (e.g., 37), in equilibrium with the silyl allenol ethers of type 38, underwent diastereoselective carbocyclization in suitable systems, providing cyclopentanol 39, for example, after acid quench and desilylation. ... 

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