Vinylogous Hydrazone Strategy for the Organocatalytic Alkylation of Heteroaromatic Derivatives

A new umpolung approach for the asymmetric FriedelCrafts-type alkylation of electron-poor heteroaromatic systems has been developed. It is based on the vinylogous reactivity of hydrazones derived from heteroaromatic aldehydes. Donating effect of the hydrazone moiety can be efficiently transferred over the heteroaromatic system activating it towards asymmetric FriedelCrafts reaction with α,β-unsaturated aldehydes realized under aminocatalytic conditions. Excellent enantioselectivities have been obtained owing to the application of MacMillan imidazolidinone catalyst. Unmasking of hydrazone moiety has been also realized resulting in the development of a unique strategy for the asymmetric functionalization of electron-poor heteroaromatic systems.