Enantioselective Metallophosphite-Catalyzed C-Acylation of Nitrones

Metallophosphites derived from tartaric acid catalyze the enantioselective addition of acyl silanes to nitrones. The product α-N-silyloxyamino ketones are obtained in moderate to good yields (36−94%) with excellent enantioselectivity (er ≥ 95:5). The nitrone oxygen is essential in facilitating the silyl transfer that is required for catalyst turnover. This represents, to the best of our knowledge, the first example of C-acylation of nitrones and the most highly enantioselective catalytic addition of an acyl anion equivalent to an azomethine electrophile. The N−O bond of the product may be reductively cleaved under mild conditions to provide N-aryl α-amino ketones with negligible loss of enantiopurity.