The Povarov reaction provides a straightforward and modular entry to 1,2,3,4-tetrahydroquinolines (THQs). Despite its importance, it was only very recently that several highly efficient catalytic asymmetric protocols for this reaction have been developed, as summarized in this review which falls on the 50 th anniversary of Povarov's pioneering disclosure. Furthermore, this review collects and critically discusses the interrupted versions of the reaction, often featuring intriguing and still unclear mechanicistic pathways.

The organocatalytic asymmetric α-alkylation of aldehydes by 1,6-conjugated addition of enamines to p-quinone methides is described. Employing a newly developed class of chiral secondary amine catalysts, α-diarylmethine-substituted aldehydes with two contiguous stereocenters have been synthesized in a simple manner with good diastereocontrol and excellent enantioselectivity.

Quinone methides (QMs) are highly reactive compounds that have been defined as "elusive" intermediates, or even as a "synthetic enigma" in organic chemistry. Indeed, there were just a handful of examples of their utilization in catalytic asymmetric settings until some years ago. This review collects organocatalytic asymmetric reactions that employ QMs as substrates and intermediates, from the early examples, mostly based on stabilized QMs bearing specific substitution patterns, to more recent contributions, which have dramatically expanded the scope of QM chemistry. In fact, it was only very recently that the generation of QMs in situ through strategies compatible with organocatalytic methodologies has been realized. This tactic has finally opened the gate to the full exploitation of these unstable intermediates, leading to a series of remarkable disclosures. Several types of synthetically powerful asymmetric addition and cycloaddition reactions, applicable to a broad range of QMs, are now available.

A new approach to the utilization of highly reactive and unstable ortho-quinone methides (o-QMs) in catalytic asymmetric settings is presented. The enantioselective reactions are catalysed by bifunctional organocatalysts, and the o-QM intermediates are formed in situ from 2-sulfonylalkyl phenols through base-promoted elimination of sulfinic acid. The use of mild Brønsted basic conditions for transiently generating o-QMs in catalytic asymmetric processes is unprecedented, and allows engaging productively in the reactions nucleophiles such as Meldrum's acid, malononitrile and 1,3-dicarbonyls. The catalytic transformations give new and general entries to 3,4-dihydrocoumarins, 4H-chromenes and xanthenones. These frameworks are recurring structures in natural product and medicinal chemistry, as testified by the formal syntheses of (R)-tolterodine and (S)-4-methoxydalbergione from the catalytic adducts.

The first example of a catalytic asymmetric vinylogous Povarov reaction is presented. 1-N-Acylamino-1,3-butadienes react selectively at their terminal double bond in the presence of a chiral phosphoric acid catalyst, delivering highly enantioenriched 1,2,3,4-tetrahydroquinolines bearing a synthetically versatile enecarbamate group at the 4-position.