Formation of Dihydronaphthalenes via Organocatalytic Enatioselective Michael–Aldol Cascade Reactions with Arylalkanes

Vinylogous and Arylogous Stereoselective Base-Promoted Phase-Transfer Catalysis

Vinylogous enolate and enolate-type carbanions, generated by deprotonation of α,β-unsaturated compounds and characterized by delocalization of the negative charge over two or more carbon atoms, are extensively used in organic synthesis, enabling functionalization and C–C bond formation at remote positions. Similarly, reactions with electrophiles at benzylic and heterobenzylic position are performed through generation of arylogous and heteroarylogous enolate-type nucleophiles. Although widely exploited in metal-catalysis and organocatalysis, it is only in recent years that the vinylogy and arylogy principles have been translated fruitfully in phase-transfer catalyzed processes. This review provides an overview of the methods developed to date, involving vinylogous and (hetero)arylogous carbon nucleophiles under phase-transfer catalytic conditions, highlighting main mechanistic aspects.

Iron-Catalyzed Ortho C-H Homoallylation of Aromatic Ketones with Methylenecyclopropanes

We report here a C-H homoallylation reaction of aromatic ketones with methylenecyclopropanes (MCPs) only using a catalytic amount of Fe(PMe₃)₄. A variety of aromatic ketones and MCPs are applicable to the reaction to form ortho-homoallylated aromatic ketones selectively via regioselective scission of the three-membered rings. The homoallylated products are amenable to further elaborations, providing functionalized 1,2-dihydronaphthalenes.

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.

Redox-Annulations of Cyclic Amines with Electron-Deficient o-Tolualdehydes

Amines such as 1,2,3,4-tetrahydroisoquinoline undergo redox-neutral annulations with 2-methyl-3,5-dinitrobenzaldehyde and closely related substrates. Acetic acid serves as the solvent and sole promoter of these transformations which involve dual C-H functionalization.

One-Pot Allylation-Intramolecular Vinylogous Michael Addition-Isomerization Cascade of o-Hydroxycinnamates and Congeners: Synthesis of Substituted Benzofuran Derivatives

A unique intramolecular vinylogous Michael addition leading to the synthesis of heterocycles has been disclosed. Base-promoted one-pot sequential O-allylation of o-hydroxy-cinnamates or -cinnamonitrile or -chalcones with γ-bromocrotonates followed by an intramolecular conjugate addition of vinylogous Michael donors resulted in the formation of highly substituted benzofuran derivatives in good to excellent yields. The intramolecular event followed by two [1,3]-H shifts leading to aromatization appears to be the key to the success of this unprecedented transformation.

A chiral-at-metal asymmetric catalyzed vinylogous Michael addition of ortho-methyl aromatic nitro compounds for isoxazole derivative synthesis

A chiral-at-metal rhodium(iii) complex catalyzed asymmetric vinylogous Michael addition of 5-methyl 4-nitroisoxazoles with α,β-unsaturated 2-acyl imidazoles has been developed, delivering the corresponding adducts with up to 96% yield and 97% ee.

Direct Asymmetric Vinylogous Mannich Addition of 3,5-Disubstituted-4-nitroisoxazoles to Isatin-Derived Imines Catalyzed by a Bifunctional Phase-Transfer-Catalyst

Asymmetric Mannich-type addition of 3,5-disubstituted-4-nitroisoxazoles to isatin-derived Boc-protected imines has been realized by using 0.01 equiv of amide phosphonium salt as a phase transfer catalyst. Our current methodology allows for the formation of 3-isoxazolylmethyl-substituted 3-aminooxindoles in excellent yields with good to excellent enantioselectivities. The practical value of this methodology was exemplified by a gram-scale synthesis of 5an, a key intermediate for the formal synthesis (+)-AG-041R.

Direct Access of the Chiral Quinolinyl Core of Cinchona Alkaloids via a Brønsted Acid and Chiral Amine Co-catalyzed Chemo- and Enantioselective α-Alkylation of Quinolinylmethanols with Enals

A strategy for the facile construction of the chiral quinolinylmethanolic structure, a core featured in cinchona alkaloids, is reported. A new reactivity is harnessed by TfOH-promoted chemoselective activation of α-C-H over O-H bond in quinolinylmethanols. The new reactivity is successfully engineered with an iminium catalysis in a synergistic manner to create a powerful conjugate addition-cyclization cascade process for synthesis of chiral quinoline derived γ-butyrolactones in good yields and with good to excellent enantioselectivities. The method enables the first total synthesis of natural product broussonetine in three steps.

Asymmetric synthesis of tetrahydroisoquinoline-fused spirooxindoles as Ras-GTP inhibitors that inhibit colon adenocarcinoma cell proliferation and invasion

We report the synthesis of a library of chiral THIQ-fused spirooxindoles. The most potent compound inhibits Ras-GTP, ultimately leading to mitochondrial apoptosis.

Co(OAc)2-Catalyzed Trifluoromethylation and C(3)-Selective Arylation of 2-(Propargylamino)pyridines via a 6-Endo-Dig Cyclization

A Co(OAc)₂-catalyzed trifluoromethylation and subsequent C(3)-selective arylation of 2-(propargylamino)pyridines has been developed. A new 6-endo-dig cyclization involving an unprecedented C(3) selective arylation of the pyridines instead of a commonly observed 5-exo-dig cyclization with "N" is realized. Moreover, the study presents the first case of the installation of a trifluoromethyl group into electron-deficient azaarenes. The process delivers an efficient cascade approach to new trifluoromethylated 1,8-naphthyridine structures with a broad substrate scope.

Asymmetric synthesis of isoquinolinonaphthyridines catalyzed by a chiral Brønsted acid

A catalytic asymmetric method for the synthesis of chiral isoquinolinonaphthyridines has been developed. A chiral disulfonimide catalyzes a redox cyclization reaction between 2-methyl-3-aldehydeazaarenes and 1,2,3,4-tetrahydroisoquinolines to deliver a range of isoquinolinonaphthyridines with good to high yields (up to 91%) and up to 92 : 8 er.

Transition-metal-free synthesis of indolizines via [3 + 2]-annulation from α-bromoenals and 2-substituted azaarenes

A transition-metal-free “one-pot” synthetic approach for the synthesis of indolizines from α-bromo-substituted enals and simple 2-substituted azaarenes has been developed.

Iron-catalyzed trifluoromethylation of vinylcyclopropanes: facile synthesis of CF3–containing dihydronaphthalene derivatives

FeCl₂-catalyzed trifluoromethylation of vinylcyclopropanes to generate a series of CF₃-containing dihydronaphthalene derivatives in moderate to high yields (up to 96%) under mild reaction conditions was successfully developed.

Enantioselective Synthesis of Highly Substituted Chromans via the Oxa-Michael-Michael Cascade Reaction with a Bifunctional Organocatalyst

A highly enantioselective synthesis of chiral chroman derivatives via an oxa-Michael-Michael cascade reaction has been developed using a bifunctional thiourea organocatalyst. The products were obtained with excellent enantioselectivities (up to >99%), good yields (up to 95%), and diastereoselectivities (up to 5:1).

Construction of an all-carbon quaternary stereocenter by organocatalytic enantioselective α-functionalization of α-substituted β-ketocarbonyls with electron deficient vinylarenes

An all-carbon quaternary stereocenter is efficiently constructed by a chiral amine catalyzed enantioselective α-functionalization of α-substituted β-ketocarbonyls with electro-deficient vinylarenes.

Efficient synthesis of tetrahydronaphthalene- or isochroman-fused spirooxindoles using tandem reactions

The cascade reaction involving a Michael–aldol or vinylogous Henry-acetalization relay is described. We have used the cascade reaction to assemble tetrahydronaphthalene- or isochroman-fused spirooxindoles and other drug-like spirocyclic scaffolds.