On-Water Vinylogous Mukaiyama-Michael Addition of Heterocyclic 2-Silyloxydienes to 1,2-Diaza-1,3-dienes: One-Pot Three-Step Entry to Functionality-Rich Pyrroles

Enantioselective direct vinylogous Michael addition for constructing enantioenriched γ,γ-dialkyl substituted butyrolactams and octahydroindoles

A nickel(II)-catalyzed asymmetric direct vinylogous Michael addition of γ-alkyl monosubstituted α,β-unsaturated butyrolactams to α,β-unsaturated carbonyl compounds has been disclosed, affording γ,γ-dialkyl substituted butyrolactams in good yields and satisfactory enantioselectivities. A tandem catalytic asymmetric vinylogous Michael addition/intramolecular Michael addition has also been developed based on this reaction, which enabled the construction of enantioenriched octahydroindoles with three consecutive stereogenic carbon centers.

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.

Exploiting the hydrophobicity of calixarene macrocycles for catalysis under “on-water” conditions

Thioureido-calixarene derivatives provide a rate acceleration for the vinylogous Mukaiyama aldol reaction (VMAR) under on-water conditions.

Beyond classical reactivity patterns: shifting from 1,4- to 1,6-additions in regio- and enantioselective organocatalyzed vinylogous reactions of olefinic lactones with enals and 2,4-dienals

Organocatalysis is shown to expand the classical reactivity pattern for conjugate addition reactions. It is demonstrated that the site selectivity can be extended from 1,4- to 1,6-additions for the enantioselective vinylogous additions of methyl-substituted vinylogous lactones to enals and 2,4-dienals. This novel reactivity is demonstrated for methyl-substituted olefinic azlactones and butyrolactones. Their synthetic potential is first highlighted by the development of the organocatalytic regioselective vinylogous 1,4-addition to enals which proceeds with a very high level of double-bond geometry control and excellent enantioselectivity. The concept is developed further for the unprecedented intermolecular enantioselective organocatalyzed vinylogous 1,6-addition to linear 2,4-dienals, by which the site selectivity of the process is extended from the β-position to the remote δ-position of the 2,4-dienal. The organocatalyst controls the newly generated stereocenter six bonds away from the stereocenter of the catalyst with a high level of enantiocontrol, and the products are obtained with full control of double-bonds configuration. The scope of these new reaction concepts is demonstrated for a series of aliphatic and aryl-substituted enals and 2,4-dienals undergoing enantioselective vinylogous reactions with methyl-substituted olefinic azlactones and butyrolactones. Furthermore, mechanistic considerations are presented which can account for the change from 1,4- to 1,6-selectivity. Finally, a number of different transformations of the optically active 1,4- and 1,6-addition products are demonstrated.

Selective synthesis of substituted pyrrole-2-phosphine oxides and -phosphonates from 2H-azirines and enolates from acetyl acetates and malonates

A simple and efficient selective synthesis of 1H-pyrrole-2-phosphine oxides 3 and -phosphonates 7 by addition of enolates derived from acetyl acetates to 2H-azirinylphosphine oxide 1 and -phosphonate 6 is reported. Nucleophilic addition of enolates derived from diethyl malonate to 2H-azirines 1 and 6 led to the formation of functionalized 2-hydroxy-1H-pyrrole-5-phosphine oxide 9 and -phosphonate 10, while vinylogous α-aminoalkylphosphine oxides 14 and -phosphonate 15 may be obtained from azirines and the enolate derived from diethyl 2-phenylmalonate. Ring closure of vinylogous derivatives 14 and 15 in the presence of base led to the formation of 1,5-dihydro-3-pyrrolin-2-ones containing a phosphine oxide 17 or a phosphonate group 18.