Anionic Brook isomerizations

The Brook isomerization is the migration of a silyl group from a carbon atom to an oxygen anion as illustrated in its simplest [1,2] form (e.g. 27 to 28 in equation 11). ... 

Similarly, the [3-1-4] annulation of the E- and Z-isomers of /3-hetero-substituted acryloylsilanes 52 with lithium enolates of a,-unsaturated methyl ketones 54 gave stereospecifically the c -6,7-cyclopentyl-5-trimethylsilyl-3-cycloheptenone 55 (equation 20). The stereospecificity in the annulation was explained by an anionic oxy-Cope isomerization of the 1,2-divinylcyclopropanediol intermediate 56, which was generated through the Brook isomerization of the initial 1,2-adduct (equation 20). 

In contrast to 1,2-migrations between C and O, there are few reports on the Brook isomerization of a-silylamine (aza-Brook isomerization). The reaction of (a-silylallyl)amine 61 with n-C4H9Li in THF at low temperatnre followed by the addition of HMPA and CH3I gives the methylated prodnct 62 in qnantitative yield. These resnlts indicate that an aza-Brook isomerization occnrs, i.e. the silyl group of 61 migrates from carbon to nitrogen and the lithinm salt of an aUyl anion 63 is produced (equation 22) . 

Nucleophilic substitution of a,/3-epoxysilanes followed by the Peterson elimination is valuable for the stereoselective synthesis of alkenes.3 The reactions with lithium phenylsulfide and diphenylphosphide form alkenyl sulfides and alkenylphosphines, respectively, in a stereospecific manner. 7-Metallo-a,/ -epoxysilanes are isomerized to a-siloxyallylmetals by anionic ring opening and subsequent Brook rearrangement (Equation... 

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