Harnessing the ambiphilicity of silyl nitronates in a catalytic asymmetric approach to aliphatic beta(3)-amino acids

Nitronate anions, formally generated by alpha-deprotonating the corresponding nitroalkanes, are highly nucleophilic and versatile intermediates in many carbon-carbon bond-forming reactions. In contrast, the corresponding silyl nitronates are ambiphilic and react, at the same carbon atom, with both electrophiles and nucleophiles. However, while their nucleophilicity has been well exploited in catalytic enantioselective reactions with imines and aldehydes, utilizing the electrophilicity of silyl nitronates in asymmetric synthesis has remained elusive. Here we report the facile, efficient and general reactivity of readily available silyl nitronates with silyl ketene acetals, catalysed by highly Lewis-acidic and confined silylium imidodiphosphorimidate catalysts. The products of this reaction, so-called nitroso acetals, are obtained in excellent enantioselectivity and can be easily converted into N-Boc-beta(3)-amino acid esters in a single step.