Asymmetric Vinylogous Aldol Reaction ofα-ketoesters with 3-alkylidene oxindoles

Asymmetric (3 + 3) and (4 + 2) Annulation Reactions of 2,3-Dioxopyrrolidines with 3-Alkylidene Oxindoles to Construct Diverse Chiral Heterocyclic Frameworks

Two substrate-controlled regiodivergent annulation protocols for 2,3-dioxopyrrolidines with 3-alkylidene oxindoles have been developed, which furnished a series of fused dihydropyrrolidone derivatives in high yields with excellent stereoselectivities. Plausible mechanistic pathways for both annulation reactions are proposed that [3 + 3] annulation reaction involves vinylogous Michael addition followed by intramolecular aldol cyclization, while [4 + 2] annulation reaction occurs through a vinylogous Michael addition and a subsequent intramolecular oxa-Michael cyclization.

Enantioselective Synthesis of Thiazolopyran Derivatives via a Direct Vinylogous Michael-oxa-Michael Sequence

An efficient diastereo- and enantioselective direct vinylogous Michael-oxa-Michael sequence between 5-alkenyl thiazolones and isopropylidene oxindoles has been developed. The reaction is catalyzed by a bifunctional squaramide catalyst that allows to access a wide range of densely substituted thiazolopyran derivatives containing a quaternary stereocenter. This protocol is flexible toward different sterically and electronically tuned substrates and is amenable to gram-scale synthesis and several synthetic transformations.

Organocatalytic Asymmetric Direct Vinylogous Michael Initiated Ring Closure Reaction of 4-Nitroisoxazole Derivatives to 3-Isopropylidene Oxindoles

Herein, we present the first ever use of 3-isopropylidene oxindoles as electrophiles in vinylogous Michael initiated ring closure reaction (MIRC). Among the various alkylidene oxindoles used in enantioselective spirocyclization reactions, isopropylidene oxindoles are the least explored to date. The competing reactivity of isopropylidene oxindoles (electrophilicity vs nucleophilicity) in the presence of a chiral organocatalyst is controlled by the logical selection of a more reactive nucleophile. The methodology produces a library of densely substituted highly enantioenriched spirocyclopropyl oxindoles with excellent yield and stereoselectivities. Moreover, the first enantioselective synthesis of HIV-1 NNRT inhibitor indicates the importance of our synthesized spiro-cyclopropyl oxindole core.

Enantioselective vinylogous Mukaiyama aldol reaction of α-ketoesters under bifunctional organocatalysis

A highly enantioselective vinylogous Mukaiyama aldol reaction to ketoesters catalysed by a hydrogen-bond-donor-based bifunctional organocatalyst is presented. The addition of silyloxy dienol ether gives rise to multifunctional chiral tertiary alcohols bearing a versatile α,β-unsaturated aldehyde with excellent enantiocontrol.

Enantioselective organocatalytic vinylogous aldol-cyclization cascade reaction of 3-alkylidene oxindoles with o-quinones

Spirocyclic o-quinone analogues show a broad spectrum of applications as biologically active compounds. We herein report the chiral bifunctional squaramide catalysed asymmetric vinylogous aldol-cyclization cascade reaction between 3-alkylidene oxindoles and o-quinones. A wide range of enantioenriched spirocyclic o-quinone analogues with a quaternary stereocenter could be smoothly synthesized in good to excellent yields (up to 99%) with high enantioselectivities (up to 99%).

Regio- and Stereoselective Synthesis of Dispiro-bisoxindoles via [3+2] Annulation Involving Nitroisatylidene as a Vinylogous Michael Donor

A cascade [3+2] annulation, involving a γ-selective vinylogous Michael addition of nitroalkylideneoxindoles to various electron deficient alkenes followed by an intramolecular Michael addition, provides access to dispiro-bis-oxindoles and spiro-oxindoles. Up to four contiguous chiral centers, including two quaternary spirocenters, are generated in this high-yield regio- and diastereoselective transformation that also provides a convenient entry into conformationally constrained γ-amino acid derivatives.

Catalytic enantioselective synthesis of chiral 4-hydroxy 4′-substituted pyrazolones by the vinylogous aldol reaction of pyrazole-4,5-diones with 3-alkylidene-2-oxindoles

Here, a bifunctional quinine-derived benzamide catalyzed direct enantioselective vinylogous aldol reaction between 3-alkylidene-2-oxindoles and pyrazole-4,5-diones has been developed.

Stereoselective formal [3 + 3] annulation of 3-alkylidene-2-oxindoles with β,γ-unsaturated α-keto esters

1,4-Diazabicyclo[2.2.2]octane (DABCO)-catalyzed [3 + 3] cycloaddition reaction of 3-alkylidene-2-oxindole and β,γ-unsaturated α-keto esters under mild reaction conditions afforded the spirocyclohexene-oxindole with excellent diastereoselectivity. The [3 + 3] annulation is found to proceed through a vinylogous Michael-aldol cascade reaction and it allows rapid access to a diverse set of highly functionalized spirocyclohexene-oxindoles. Also, a bioactivity study of the compounds on mammalian sarcoma cells has reflected cell growth inhibitory/anti-cancer properties.

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.

Direct Catalytic Asymmetric Synthesis of Oxindole-Derived δ-Hydroxy-β-ketoesters by Aldol Reactions

Direct asymmetric synthesis of δ-hydroxy-β-ketoesters was accomplished via regio- and enantioselective aldol reactions of β-ketoesters with isatins catalyzed by cinchona alkaloid thiourea derivatives. The C-C bond formation of the reactions occurred only at the γ-position of the β-ketoesters. Reaction progress monitoring and product stability analyses under the conditions that included the catalyst indicated that the γ-position reaction products were formed kinetically. Various δ-hydroxy-β-ketoesters bearing 3-alkyl-3-hydroxyoxindole cores relevant to the development of bioactive molecules were synthesized.