Catalyst-Controlled Diastereoselectivity Switch in the Asymmetric [3 + 2] Annulation of Isatin-Derived MBH Carbonates and 5-Alkenylthiazol-4(5H)-ones

Asymmetric Organocatalytic Diels-Alder Reaction of Olefinic Azlactones with Unsaturated Thiazolones: Access to Spirocyclohexenone Thiazolone Skeletons

Chiral bifunctional thiourea-catalyzed Diels-Alder reaction between olefinic azlactones and alkylidene thiazolone derivatives is reported here for the first time. The asymmetric Diels-Alder reaction delivers vicinal tertiary-quaternary stereocenters in spirocyclohexenone thiazolones in moderate to high yields and good stereochemical outcomes. The protocol can be adapted to a broad array of substrates. Moreover, the reaction is scaled up, and the chiral spirocyclohexenone thiazolone was converted into valuable spirocyclic-1,2-amidoalcohol highlighting the synthetic utility of our methodology.

Ag(I)-catalyzed asymmetric (2+4) annulation reaction of 5-alkenyl thiazolones: synthesis of enantioenriched spiro[cyclohexenamines-thiazolones]

The first metal-catalyzed (2+4) annulation of 5-alkenyl thiazolones and α,α-dicyanoalkylidenes has been developed via vinylogous Michael/cyclization/isomerization reaction. This (2+4) annulation reaction is catalyzed by a chiral Ag-(R)-DTBM-SEGPHOS catalyst, delivering enantioenriched spiro[cyclohexenamines-thiazolone] having contiguous quaternary and tertiary stereocenters in good to excellent yield (up to 80%) and excellent stereoselectivities (up to 97% ee and >20 : 1 dr). This methodology has high functional group tolerance and produces a broad range of enantioenriched products under mild reaction conditions.

Substrate-Controlled Diversity-Oriented Synthesis of Novel Polycyclic Frameworks via [4 + 2] and [3 + 2] Annulations of Ninhydrin-Derived MBH Adducts with 3,4-Dihydroisoquinolines

Substrate-controlled diversity-oriented synthesis of polycyclic frameworks via [4 + 2] and [3 + 2] annulations between ninhydrin-derived Morita-Baylis-Hillman (MBH) adducts and 3,4-dihydroisoquinolines under similar reaction conditions have been developed. The reaction provides diversity-oriented synthesis of a series of novel and structurally complex spiro multi heterocyclic skeletons in good yields (up to 87% and 90%, respectively) with excellent diastereoselectivities (up to >25:1 dr). In particular, the switchable [4 + 2] and [3 + 2] annulation reactions are controlled by tuning the hydroxyl protecting group on the ninhydrin-derived MBH adduct to deliver structural diverse spiro[indene-2,2'-[1,3]oxazino[2,3-a]isoquinoline] and spiro[indene-2,1'-pyrrolo[2,1-a]isoquinoline], respectively. Furthermore, the relative configuration and chemical structure of two kinds of cycloadducts were confirmed through X-ray diffraction analysis.

Substrate-Controlled Diastereo- and Enantiodivergent Synthesis of Bis-Spirocyclopropyloxindoles from Available Isatin as a Single Starting Material

The first diastereo- and enantiodivergent asymmetric synthesis of new bis-spirocyclopropyloxindole scaffolds has been accomplished from the readily available isatin as a single starting material. Four rel-(1R,2R,3R), rel-(1S,2S,3R), rel-(1R,2R,3S), and rel-(1S,2S,3S) configurations of desired products were constructed in excellent enantiopurity via a simple switch in substrates using the chiral auxiliary-controlled method. The absolute configuration of cycloadducts with three contiguous quaternary/tertiary stereogenic centers was confirmed through X-ray diffraction analysis. A facile synthesis of versatile precursor 3-chlorooxindoles was also introduced.

Divergent Synthesis of Highly Substituted Tetrahydroquinolines and Cyclopentenes via Lewis Base Catalyzed Switchable [4 + 2] and [3 + 2] Annulations of MBH-Carbonates with Activated Olefins

A highly selective and divergent synthesis which enabled access to various complex compounds is highly attractive in organic synthesis and medicinal chemistry. Herein, we developed an effective method for divergent synthesis of highly substituted tetrahydroquinolines via Lewis base catalyzed switchable annulations of Morita-Baylis-Hillman carbonates with activated olefins. The reaction displayed switchable [4 + 2] or [3 + 2] annulations via catalyst or substrate control, providing a diverse range of architectures which contained highly substituted tetrahydroquinolines or cyclopentenes with three contiguous stereocenters bearing a quaternary carbon center in high yields with excellent diastereoselectivities and regioselectivities. Furthermore, synthetic utility of this strategy was further highlighted by gram-scale experiments and simple transformations of the products.

Asymmetric synthesis of the perhydroepoxyethanoindole core via sequential [4 + 2]-addition/reduction/fluoroannulation reactions

Herein, we present the sequential aminocatalytic [4 + 2]-addition/reduction and fluoroannulation reactions to afford a novel class of bridged fluoro-perhydroepoxyethanoindole spiropyrazolone and fluoro-perhydroepoxyethanoindole spirooxindole moieties with six contiguous stereocenters. An array of perhydroepoxyethanoindole core derivatives (up to 31 examples) mimicking aspidosperma alkaloids were obtained with moderate to good yields and excellent enantio- and diastereo-selectivities (up to 69% overall yield, up to 99.9% ee and up to >20 : 1 dr). Furthermore, we have also disclosed the synthesis of the unexpected tribromo derivative of hexahydroepoxyethanoindole spiropyrazolone in a moderate yield with excellent selectivity by employing the developed protocol in sequential bromoannulation reactions.

Asymmetric α-Regioselective [3 + 2] Annulation of Morita-Baylis-Hillman Carbonates: Construction of Three Contiguous Stereocenters with Vicinal Quaternary Carbon Centers

Asymmetric α-regioselective annulation of MBH carbonates with 4-arylmethylisoxazol-5-ones has been developed to afford spirocyclic oxindole derivatives containing three contiguous stereogenic centers and vicinal all-carbon quaternary chiral centers. This reaction exhibits a broad substrate scope and excellent functional group tolerance. Excellent yields with high diastereo- and enantioselectivities were obtained in this efficient organocatalytic reaction.

Diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones via tuneable Lewis base/Brønsted base-promoted (3 + 2) cycloadditions

We have developed unique base-promoted diastereoselective (3 + 2) cycloadditions. A diastereodivergent synthesis of fully disubstituted spiro[indoline-3,2′-pyrrolidin]-2-ones was realized by tuning a Lewis base/Brønsted base.

Organocatalytic asymmetric synthesis of multifunctionalized α-carboline-spirooxindole hybrids that suppressed proliferation in colorectal cancer cells

An asymmetric organocatalytic cascade reaction has been reported for the rapid assembly of multifunctionalized α-carboline-spirooxindole hybrids, which suppressed proliferation in colorectal cancer cells.

Recent Advances in Lewis Base-Catalysed Chemo-, Diastereo- and Enantiodivergent Reactions of Electron-deficient Olefins and Alkynes

Lewis base catalysis provides powerful synthetic strategies for the selective construction of carbon-carbon and carbon-heteroatom bonds. Thus continuous efforts have been deployed to develop effective methodologies involving Lewis base catalysis. The nucleophilicity and steric hindrance of Lewis base catalyst often plays a major role in catalytic reactivity and selectivity in the reaction. In the past decades, tremendous progress has been made in the divergent construction of valuable motifs under Lewis base catalysis. In this review, we provide a comprehensive and updated summary of Lewis base-catalysed chemo-, diastereo- and enantiodivergent reaction, as well as the related mechanism will be highlighted in detail.