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N,O-aminals, molecules bearing a geminally N,O-substituted (stereogenic) carbon center, have been recently recognized as an important class of building blocks in organic synthesis. As direct precursors of imines and iminium ions, N,O-aminals were converted through asymmetric organocatalysis or metal catalysis to diverse enantiomerically enriched compounds including N-heterocycles. Furthermore, cyclic N,O-hemiaminals acted as acyclic amino aldehyde surrogates, which were transformed to enantioenriched products otherwise challenging to access. Finally, cyclic N,O-aminals were formed in situ as key intermediates in asymmetric catalysis. In this review, we introduce a wide array of catalytic asymmetric protocols involving the use of four distinct types of N,O-aminals as starting materials or key intermediates.

Asymmetric C(sp)-C(sp(2)) bond formation to give enantiomerically enriched 1,3-butadienyl-2-carbinols occurred through a homoallenylboration reaction between a 2,3-dienylboronic ester and aldehydes under the catalysis of a chiral phosphoric acid (CPA). A diverse range of enantiomerically enriched butadiene-substituted secondary alcohols with aryl, heterocyclic, and aliphatic substituents were synthesized in very high yield with high enantioselectivity. Preliminary density functional theory (DFT) calculations suggest that the reaction proceeds via a cyclic six-membered chairlike transition state with essential hydrogen-bond activation in the allene reagent. The catalytic reaction was amenable to the gram-scale synthesis of a chiral alkyl butadienyl adduct, which was converted into an interesting optically pure compound bearing a benzo-fused spirocyclic cyclopentenone framework.

The Perkin condensation of acid (IV) with aldehyde (V) followed by a copper-promoted decarboxylation and subsequent demethylation-isomerization reaction gives rise to resveratrol (VIIIa).

The η6-hydroquinone iridium complex [(η6-H2Q)Ir(COD)]BF4 undergoes facile double deprotonation to the η4-quinone anionic analogue. The latter has been shown to be the first example of an iridium complex that catalyzes 1,4 conjugate addition reactions of aryl boronic acids to electron deficient olefins.