Catalytic and asymmetric Michael reactions constitute very powerful tools for the construction of new C-C bonds in synthesis, but most of the reports claiming high selectivity are limited to some specific combinations of nucleophile/electrophile compound types, and only few successful methods deal with the generation of all-carbon quaternary stereocenters. A contribution to solve this gap is presented here based on chiral bifunctional Brønsted base (BB) catalysis and the use of α'-oxy enones as enabling Michael acceptors with ambivalent H-bond acceptor/donor character, a yet unreported design element for bidentate enoate equivalents. It is found that the Michael addition of a range of enolizable carbonyl compounds that have previously demonstrated challenging (i.e., α-substituted 2-oxindoles, cyanoesters, oxazolones, thiazolones, and azlactones) to α'-oxy enones can afford the corresponding tetrasubstituted carbon stereocenters in high diastereo- and enantioselectivity in the presence of standard BB catalysts. Experiments show that the α'-oxy ketone moiety plays a key role in the above realizations, as parallel reactions under identical conditions but using the parent α,β-unsaturated ketones or esters instead proceed sluggish and/or with poor stereoselectivity. A series of trivial chemical manipulations of the ketol moiety in adducts can produce the corresponding carboxy, aldehyde, and ketone compounds under very mild conditions, giving access to a variety of enantioenriched densely functionalized building blocks containing a fully substituted carbon stereocenter. A computational investigation to rationalize the mode of substrate activation and the reaction stereochemistry is also provided, and the proposed models are compared with related systems in the literature.

The catalytic asymmetric synthesis of both α-substituted and α,α-disubstituted (quaternary) β-tetralones through direct α-functionalization of the corresponding β-tetralone precursor remains elusive. A designed Brønsted base-squaramide bifunctional catalyst promotes the conjugate addition of either unsubstituted or α-monosubstituted β-tetralones to nitroalkenes. Under these reaction conditions, not only enolization, and thus functionalization, occurs at the α-carbon atom of the β-tetralone exclusively, but adducts including all-carbon quaternary centers are also formed in highly diastereo- and enantioselective manner.

A catalytic and highly stereoselective entry to propargylic alcohols and products derived thereof is reported based on an unprecedented cross-aldol coupling between unmodified aldehydes and ynals. The method requires an amine-metal salt-Brønsted acid ternary catalyst system and implies synergistic activation of the donor aldehyde via enamine and of the acceptor carbonyl via unique and reversible metal-alkyne complexation. Specifically, by using a combined a,a-dialkylprolinol silyl ether-CuI-PhCO 2 H catalyst system, remarkably high levels of diastereo-and enantioselectivity (anti/syn up to >20 : 1, ee up to >99%) are achieved.

In this study, the unique capacity of bifunctional Brønsted bases to generate α‐branched ketone dienolates and control both site‐ and stereoselectivity of their addition reactions to representative classes of carbon electrophiles (i.e., vinyl sulfones, nitroolefins, formaldehyde) is documented. We demonstrate that by using selected chiral tertiary amine/squaramide catalysts, the reactions of β,γ‐unsaturated cycloalkanones proceed through the dienolate Cα almost exclusively and provide all‐carbon quaternary cyclic ketone adducts in good yields with very high enantioselectivities. A minor amount (<5 %) of γ‐addition is observed when nitroolefins are used as electrophiles. The parent acyclic ketone dienolates proved to be less reactive under these conditions, and thus still constitute a challenging class of substrates. Quantum chemical calculations correctly predict these differences in reactivity and explain the observed site‐specificity and enantioselectivity.

Here we report the highly enantio-and syn-selective synthesis of β-hydroxy α-amino acids from glycine imine derivatives under Brønsted base (BB) catalysis. The key of this approach is the use of benzophenone-derived imine of glycine o-nitroanilide as a pronucleophile, where the o-nitroanilide framework provides an efficient hydrogen-bonding platform that accounts for nucleophile reactivity and diastereoselectivity.