New Lewis-basic N-oxides as chiral organocatalysts in asymmetric allylation of aldehydes

Allylation of aromatic and heteroaromatic aldehydes 1a-k with allyltrichlorosilane 2 can be catalyzed by the new heterobidentate, terpene-derived bipyridine N-monoxides 4, 6a,b, and 8-11 (less than or equal to 10 mol %) to afford (S)-(-)-3 with high enantioselectivities (less than or equal to99% ee). The stereochemical outcome has been found to be controlled by the axial chirality of the catalyst, which in turn is determined by the central chirality of the annulated terpene units. Solvent effects on the conversion and the level of asymmetric induction have been elucidated, and MeCN has been identified as the optimal solvent for these catalysts.