Brook rearrangement methyl ketone enolate

Some /J-heteroatom substituted a,/J-unsaturated acyl silanes react with methyl ketone enolates in a stepwise stereoselective cyclopentannelation process, formally a [3 + 2] annelation, which may proceed through aldol reaction followed by Brook rearrangement and cyclization (Scheme 111)223. 

Ab initio through-space/bond interaction analysis was applied to 3 + 2-anulation based on Brook rearrangement using /i-phcnylthioacryloylsilanes with alkyl methyl ketone enolates (Scheme 103).150 The major product has the large substituents on the same side of the five-membered ring. Orbital interactions related to the carbanion... 

In an interesting transformation, reaction of benzoyl trimethylsilane with lithium enolates derived from various methyl ketones gives rise to 1,2-cyclopropanediols, predominantly with the cis configuration, in good yields (Scheme 77). The reaction, which proceeds through addition, Brook rearrangement and cyclization, is also successful with a,/l-unsaturated acyl silanes vide infra, Section IV.D)187. 

Similarly, the [3 + 4] annulation of the E- and Z-isomers of /1-heteroatom-substituted acryloylsilanes 156 with lithium enolates of ,/l-unsaturated methyl ketones 157 gave stereospecifically cis-5,6- and //r/w.v-5,6-disubstituted-3-cycloheptenones 160, respectively (equation 97). The stereospecificity in the annulation was explained by an anionic oxy-Cope rearrangement of the 1,2-divinylcyclopropanediol intermediate 159, which was generated through the Brook rearrangement of the initial 1,2-adduct 158219 - 223. 

Tandem Carbon-Carbon Bond Formation via Brook Rearrangement Takeda et al. have reported that the reactions of benzoyl- and crotonylsilanes with hthium enolates of methyl ketones produce 1,2-cyclopropanediol monosilyl ethers via the Brook rearrangement of the initial 1,2-adduct 158 and the subsequent internal nucleophilic addition (Scheme 10.225) [587]. No formation of the corresponding cyclopropanes with alkanoylsilanes implies fhat fhe Brook rearrangement is accelerated by the phenyl or vinyl group. 

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