Allenylsilanes, electrophilic substitution reactions

AUcylidene triphenylphosphoranes, synthesis and reactions of, 14, 3 Allenylsilanes, electrophilic substitution reactions of, 37, 2... 

It is also possible to employ trimethylsilyl-substituted propargylic trichlorosilanes in electrophilic substitution reactions leading to allenylsilanes (Eq. 9.45) [50]. The trichlorosilanes can be prepared by SN2 or SN2 displacement of allenic or propargylic bromides by a trichlorosilyl copper reagent. The overall process, starting from an enantioenriched propargylic bromide of unknown enantiopurity, afforded a racemic allenylsilane (Eq. 9.46)... 

Allenylsilanes may behave as allyl or vinylsilanes. In general, allylsilane behaviour dominates over vinylsilane behaviour. The reactions of allenylsilanes with electrophiles have been comprehensively reviewed by Fleming, Dunogues and Smithers118. Electrophilic substitution of allenylsilanes gives alkynes (equation 106)173. 

The reaction of allenylsilanes with electrcm deficient ir-systems constitutes a powerful and general method for the regio- and stereo-selective preparation of substituted cyclopentenes. As first reported, (trimethylsilyl)allenes function as three-carbon nucleophiles in TiCU-promoted (trimethylsilyl)cycIopen-tene annelations (Scheme 31). The annelation process involves the polarization of an a, -unsaturated carbonyl compound by TiCU to generate an alkoxyallylic cation. Regiospecific electrophilic substitution of this cation at C-3 of the allenylsilane produces a silicon-stablized vinyl cation. A 1,2-shift of the tri-... 

Research in the laboratory of R.L. Danheiser has shown that allenylsilanes can be reacted with electrophiles other than enones, such as aldehydes and A/-acyl iminium ions to generate oxygen and nitrogen heterocycles." Aldehydes can function as heteroallenophiles and the reaction of C3 substituted allenylsilane with the achiral cyclohexane carbaldehyde afforded predominantly c/s-substituted dihydrofurans. 

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