Chiral Ammonium Betaines as Bifunctional Organocatalysts

Significance

The authors established a new ammonium betaine catalyst in asymmetric Mannich-type reactions. The reaction of α-nitrocarboxylates with N-Boc imines proceeded in the presence of catalyst 1 in excellent yields and enantioselectivities, albeit diastereoselectivities of the products were only moderate, in favor of the syn isomer. Although the activity was comparable to betaine 1, almost no stereoselectivity was observed when catalyst 2 was used. This points out the crucial role of the betaine structure, since it is able to form a structured ion pair in the reaction course.