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Abstract:
Enzymatic stereoselectivity has typically been unrivalled by most chemical catalysts,
especially in the conversion of small substrates. According to the ‘lock-and-key
theory’1,2, enzymes have confned active sites to accommodate their specifc reacting
substrates, a feature that is typically absent from chemical catalysts. An interesting
case in this context is the formation of cyanohydrins from ketones and HCN, as this
reaction can be catalysed by various classes of catalysts, including biological,
inorganic and organic ones3–7. We now report the development of broadly applicable
confned organocatalysts for the highly enantioselective cyanosilylation of aromatic
and aliphatic ketones, including the challenging 2-butanone. The selectivity (98:2
enantiomeric ratio (e.r.)) obtained towards its pharmaceutically relevant product is
unmatched by any other catalyst class, including engineered biocatalysts. Our results
indicate that confned chemical catalysts can be designed that are as selective as
enzymes in converting small, unbiased substrates, while still providing a broad scope.
