Asymmetric Intermolecular Stetter Reaction of Enals with Nitroalkenes

Significance

An asymmetric intermolecular ­Stetter reaction of enals 2 with nitroalkenes 3 catalyzed by chiral N-heterocyclic carbenes has been developed. With precatalyst 1, the reaction proceeded with good to high enantioselectivity and afforded good yields of Stetter products 4. The presence of catechol as an additive was crucial for the reaction efficiency. This effect of a bifunctional Brønsted acid has also been observed in the intramolecular Stetter reaction and could be general, enabling lower catalyst loadings in other N-heterocyclic carbene catalyzed transformations. Primary alkyl-substituted nitroalkenes are not suitable substrates for the current catalytic system.