Brook rearrangements olefination

The spirocompounds 34 (M = Ti or Zr) have been prepared . Studies of the thermolysis of pentacoordinate 1,2-oxasiletanides 35, potential intermediates in both the Peterson reaction and the homo-Brook rearrangement of p-hydroxyalkylsilanes with bases, in the presence of a proton source afforded the olefin, RCH=C(CF3)2 and/or the alcohol, (CF3)2CHOH <99CL1139>. 

Aldehydes, RCHO, have been reductively olefinated (to /ran -RCH=CHR) using chromium dichloride and trichlorosilane, apparently via a novel chromium Brook rearrangement.189 In one case, a trans- 1,2-diol (a putative intermediate in such a mechanism) was isolated. 

Fiirstner and coworkers revealed a competition between the Brook rearrangment and the Peterson olefination. The adducts of aroylsilanes 161 with (trimethylsilyl)methyl-magnesium chloride 162 underwent a Brook rearrangement and then a Peterson elimination affording vinylsilane 163 (equation 98). On the other hand, the reaction of cycloalkylcarbonylsilane 164 with 162 gave vinylsilane 165 via the direct Peterson elimination (equation 99)228. 

A homo-Peterson process intervened upon 1,4-rearrangement of the alkoxide formed by addition of tris(trimethylsilyl)methyllithium 124 to styrene oxide. The resulting carbanion 125 led mainly to the homo-Peterson product 126, with some of the adduct 127 from addition to a second equivalent of the epoxide. In their report, Fleming and co-workers noted that the homo-Peterson reaction is probably favored in this case by the benzylic positioning of the silyloxy group in 125, and they discussed the parallel between the Peterson olefination and a 1,3-Brook rearrangement process. ... 

Leighton and co-workers used the 1,4-Brook rearrangement of a vinyl ter -butyldimethylsilane 130 in their total synthesis of dolabelide D. Deprotonation of the allylic alcohol at low temperature, followed by the addition of copper(I) and DMPU, enabled the silyl transfer, and methylation of the vinylcopper provided ( )-trisubstituted olefin 131 in excellent yield. ... 

DeglTnnocenti and co-workers established in 1987 that acylsilanes could react with activated olefins in a cyanide-catalyzed sila-Stetter reaction, and recent work by Scheldt and co-workers has established the utility of thiazolylidine catalysts in this Stetter variation." The reaction is presumed to occur via a catalyst-initiated [l,2]-Brook rearrangement, which serves to provide the silylated acylanion donor intermediate 23. The use of excess 2-propanol in the reaction facilitates silyl transfer and catalyst turnover. Compared to the classical Stetter approach, this variation provides comparable yields of 1,4-diketone products from aromatic (20) and aliphatic (21) acylanion precursors. 

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