Deciphering Asymmetric Brønsted Base-Aminocatalytic Mode in Pudovik/[1,2]-Phospha-Brook Rearrangement/Michael Cascade Reaction

An approach involving the use of a bifunctional aminocatalyst containing Brønsted base and iminium activation sites for asymmetric multicomponent reactions involving [1,2]-phospha-Brook rearrangement has yet to be realized. Herein, we present an aminocatalytic enantioselective conjugate addition of α-phosphonyloxy enolates formed via [1,2]-phospha-Brook rearrangement to α,β-unsaturated ketones. The methodology unfolds a simple one-pot operation consisting of a robust additive-free catalytic system providing a series of oxindole derivatives having two contiguous stereocenters in high yields with excellent stereoselectivities.

Catalyst-Controlled Divergent Synthesis of 2H-Chromenes via [3 + 3] Annulation of Vinyl Sulfoxonium Ylides with Quinones

Herein, we report the synthesis of 2H-chromenes via catalyst-controlled highly regioselective [3 + 3] annulation of vinyl sulfoxonium ylides with quinones. Under boron-catalyzed conditions, the reaction between the ylide and quinone resulted in the formation of 2H-chromene-4-carboxylates. In contrast, a different mechanistic pathway was observed when utilizing a Ru(II) catalytic system, which led to the formation of 2H-chromene-2-carboxylates through a furan intermediate.

Enamine/Iminium-based Dual Organocatalytic Systems for Asymmetric Catalysis and Synthesis

The rational combination of two catalysts to expedite the construction of chiral complex biologically and pharmacologically relevant chiral compounds has widely gained momentum over the past decade. In particular, enamine or iminium catalysis ensuing from the activation of aldehyde or ketone by chiral amine catalysts in conjugation with other organocatalytic cycles has facilitated several asymmetric transformations to yield the enantioenriched products. Regardless of the considerable discussion on the various dual catalytic approaches, literature lacks a comprehensive review focusing on the enamine and iminium-based dual organocatalytic systems. Thus, this review article has discussed the noteworthy achievements in the field of asymmetric catalysis and synthesis catalyzed by the enamine and iminium-based dual organocatalytic systems.

Silyldienolates in Organocatalytic Enantioselective Vinylogous Mukaiyama-Type Reactions: A Review

Mukaiyama aldol, Mannich, and Michael reactions are arguably amongst the most important C-C bond formation processes and enable access to highly relevant building blocks of various natural products. Their vinylogous extensions display equally high potential in the formation of important key intermediates featuring even higher functionalization possibilities through an additional conjugated C-C double bond. Hence, it is much desired to develop highly selective vinylogous methods in order to enable unconventional, more efficient asymmetric syntheses of biologically active compounds. In this regard, silyl-dienolates were discovered to display high regioselectivities due to their tendency toward γ-additions. The control of the enantio- and diastereoinduction of these processes have been for a long time dominated by transition metal catalysis, but it received serious competition by the application of organocatalytic approaches since the beginning of this century. In this review, the organocatalytic applications of silyl-dienolates in asymmetric vinylogous C-C bond formations are summarized, focusing on their scope, characteristics, and limitations.

Stereoselective Synthesis of Spiro-α-methylene-γ-lactams via Chiral Quaternary 3-Aminooxindole Adducts Accessed by Zn-Mediated Allylation of Sulfinyl Ketimines

An efficient method for the stereoselective synthesis of α-methylene-γ-lactams via quaternary 3-aminooxindoles with very high selectivity (up to 98% ee) is described. The methodology leads to the construction of sterically congested chiral quaternary 3-aminooxindole adducts in good yield and with moderate to excellent diastereoselectivity (dr up to 95:5). The relative stereochemistry of the chiral quaternary 3-aminooxindoles adduct and the spiro-α-methylene-γ-lactam was confirmed to be syn by single-crystal X-ray structure analysis. Furthermore, the α-methylene-γ-lactam was successfully transformed into a range of chiral synthons.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

A vinylogous Michael addition-triggered quadruple cascade reaction for the enantioselective generation of multiple quaternary stereocenters

An efficient organocatalytic vinylogous Michael addition-triggered quadruple cascade reaction resulting in fused spiroxindoles bearing multiple quaternary stereocenters is demonstrated from β-trifluoroacetylarylidene indanediones and 3-alkylideneoxindoles.

Enantioselective Mukaiyama-Michael Reaction Catalyzed by a Chiral Rhodium Complex Based on Pinene-Modified Pyridine Ligands

The rhodium complex Λ-Rh1 containing chiral pinene-modified pyridine ligands is prepared through a two-step synthetic procedure; it exhibits excellent reactivity and enantiocontrol towards the enantioselective Mukaiyama-Michael reaction of α,β-unsaturated 2-acyl imidazoles with silyl enol ethers, affording enantioenriched 1,5-dicarbonyl compounds in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee).

An asymmetric vinylogous Mukaiyama–Michael reaction of α,β-unsaturated 2-acyl imidazoles catalyzed by chiral Sc(iii)– or Er(iii)–pybox complexes

A highly diastereo- and enantioselective vinylogous Mukaiyama–Michael reaction of silyloxyfurans with α,β-unsaturated 2-acyl imidazoles catalyzed by either chiral Sc(iii) or Er(iii) complexes of a pybox ligand has been reported.

Direct Diastereo- and Enantioselective Vinylogous Michael Additions of Linear Enones

A direct vinylogous Michael addition using linear vinylogous Michael donors has been developed. Notably, even γ-substituted Michael donors cleanly afforded γ-alkylated products in high yield and ee by this method. Moreover, control experiments revealed that, for these and related linear vinylogous Michael donors, the size of the Michael acceptor strongly influences whether α- or γ-alkylation occurs, not simply blocking effects of cocatalysts as suggested previously.