Imines silyl ketene

Mermerian AH, Fu GC (2005) Nucleophile-catalyzed asymmetric acylations of silyl ketene imines application to the enantioselective synthesis of verapamil. Angew Chem Int Ed 44 949-952... 

Silyl ketene imines have been acylated asymmetrically by anhydrides evidence for a silyl-free nitrile anion intermediate is discussed.86 An aza-Baylis-Hillman reaction of N-sul fonated imines is described below. 

Fu has demonstrated that acetate anion attack on the silicon center of the silyl ketene acetal, as well as formation of an acyl pyridinium salt, contribute towards the promotion of these reactions [62]. Additionally, silyl ketene imines have also been shown to participate in analogous asymmetric C-acylation reactions to yield chiral quaternary nitriles, and this method was employed as a key step in the synthesis of verapamil [65]. 

P-Hydroxyalkanitriles containing a chiral quaternary a-carhon atom are available from condensation of A-silyl ketene imines with aldehydes. The process is mediated by SiCLt, and chiral information comes from 69. ... 

Scheme 21.18 Reactions with silyl ketene imines.

Silyl ketene imines 21.126 (Scheme 21.18) developed by Denmark represent another group of useful nucleophilic reagents. These compounds are derived from protected cyanohydrins and thus can be viewed as acyl anion equivalents. They allow enantio- and diastereoselective construction of highly functionalised adducts 21.127, which can be further converted into useful synthetic intermediates, e.g. upon hydrolysis they produce crossbenzoin condensation products 21.128. ... 

Acylhydrazones, R CH=N-NHCOR , undergo stereoselective Mannich reactions with silyl ketene acetals to give j8-hydrazido esters, using activation by a chiral silicon Lewis acid. Alternatively, the use of silyl ketene imine gives a /3-hydrazido nitrile. Enantioselective (5)-l-amino-2-methoxymethylpyrrolidine (SAMP) hydrazone alkylation of aldehydes and ketones is the subject of a computational study, providing a useful screening method for possible new candidates. " ... 

Table 6 Catalytic, enantioselective additions of silyl ketene imines to 2-naphthaldehyde...

This hypothesis is further supported by the observation that conjugated silyl ketene imines (derived from unsaturated nitriles) react efficiently and selectively with aliphatic aldehydes at the less hindered y-carbon. Wilson TW unpublished results from these laboratories. 

Denmark SE, Wilson TW, Burk MT, Heemstra JR (2(X)7) Enantioselective construction of quaternary stereogenic caarbons by the lewis base catalyzed additions of silyl ketene imines to aldehydes. J Am Chem Soc 127 14864-14865... 

The thriving chemistry of ketenimines has been reviewed and an overview of the development of silyl ketene imines and their recent applications in catalytic, enantioselective... 

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