Silylallyl anions

Reaction of silylallyl anions 16 with alkyl halides gives a mixture of a- and /-alkylated products 17 and 18, respectively (equation ll)19. The ratio of y/a alkylation increases along with the bulk of the silyl groups by following the order shown in entry 8 of Table 1. 

The use of silylallyl anion in organic synthesis has been extensive24,29. The regio-and stereochemistry of these reactions can be controlled. For example, alkylation of the anion generated from the corresponding allylsilane with an electrophile E+ takes place selectively at the /-position due to steric hindrance (equation 197)352. 

The Peterson reaction has been successfully employed using a-silylallyl anions (162a and 162b Figure 17). 

In addition reactions to carbonyl compounds C-3 attack generally predominates,as illustrated in Scheme 72 with the formation of vinylsilane (163). C-1 addition also predominates in alkylation and acylation reactions involving a-silylallyl anions when alkyl halides and acyl halides are used as electrophiles. 

Reactions of ambident silyl-substituted anions The Peterson reaction has also been performed using a-silylallyl anions. 

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) . 

The reaction (equation 106) of (o -silylallyl)amines 176 with n-BuLi in THF and HMPA followed by quenching the resulting allylic anion 178 by Mel provided the corresponding iV-silyl(vinyl)arnines 177 quantitatively240. 

Aza-Brook rearrangement. (a-Silylallyl)amines undergo the rearrangement to rmerate the functionalized allyl anions, which, on alkylation and acid hydrolysis, lead to. ..nstituted aldehydes. 

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