Brook rearrangement cyanide initiation

Scheme 6,18 Formation of Q-silylcyanohydrins by cyanide ion-initiated Brook rearrangement under phase-transfer catalytic conditions.

Explored initially by Reich,cyanide addition to acyl silanes can produce Brook rearrangement, leading to an additional cascade of steps in appropriately designed systems. For example, Takeda, using a crown ether as a phase transfer agent but under non-aqueous conditions, showed that cyanide addition to acyl silanes and subsequent Brook rearrangement led, in the case of y bromo acyl silane 59 to intramolecular alkylation and formation of cyclopropanone cyanohydrin derivative 60. ... 

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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