Phosphine-catalyzed (3+3) annulation of cinnamaldehyde-derived Morita-Baylis-Hillman carbonates with dinucleophiles

The phosphine-catalyzed (3+3) annulation reaction of cinnamaldehyde-derived Morita-Baylis-Hillman (MBH) carbonates with 1,3-dicarbonyl compounds as dinucleophiles has been developed, giving hexahydrochromenone derivatives in high yields with moderate to good diastereoselectivities. The reaction worked through double conjugate addition of 1,3-dicarbonyl compounds to the phosphonium intermediates generated from the cinnamaldehyde-derived MBH carbonates.

Catalyst-free reaction of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates: synthesis of 1,2-dihydroquinolines and 2,3-dihydropyrroles

Catalyst-free annulations of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates have been successfully achieved under mild conditions. Specifically, the reaction of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with sulfur ylides furnished various 1,2-dihydroquinolines in generally high yields. Furthermore, [3+2]-annulations of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with α,β-unsaturated imines afforded a broad scope of polysubstituted 2,3-dihydropyrroles with high efficiency.

Facile synthesis of 2-vinylindolines via a phosphine-mediated α-umpolung/Wittig olefination/cyclization cascade process

A novel phosphine-mediated α-umpolung/Wittig olefination/cyclization cascade process between o-aminobenzaldehydes and Morita-Baylis-Hillman (MBH) carbonates has been ingeniously developed. This protocol serves as a practical tool for the facile synthesis of a broad range of 2-vinylindolines in moderate to good yields under mild reaction conditions. The applicability of this method was demonstrated with gram-scale reaction and various transformations of the corresponding product.

Phosphine-Catalyzed Stereospecific and Enantioselective Desymmetrizative [3+2] Cycloaddition of MBH Carbonates and N-(2-tert-Butylphenyl)maleimides

Herein, we report an l-valine-derived amide phosphine-catalyzed [3+2] cyclization of MBH carbonates and N-(2-tert-butylphenyl)maleimides via asymmetric desymmetrization. Bicyclic N-aryl succinimide derivatives bearing three continuous chiral centers with a remote C-N atropisomeric chirality were constructed stereospecifically and enantioselectively. A wide variety of MBH carbonates could be employed in this process to deliver highly optically pure succinimide derivatives in moderate to excellent yields.

Phosphine-Catalyzed (4 + 2) Annulation of Allenoates Bearing Acidic Hydrogen with 1,1-Dicyanoalkenes

α-succinimide-substituted allenoates were employed as phosphine acceptors in phosphine-catalyzed (4 + 2) annulation with 1,1-dicyanoalkenes. They served as C4 synthons in the annulation reaction under mild reaction conditions and produced hexahydroisoindole derivatives in moderate to high yields with good to excellent diastereoselectivities.

Uracil-Cu(i) catalyst: allylation of cyclopropanols with Morita-Baylis-Hillman alcohols under water-tolerant conditions

Inspired by the high affinity of copper with DNA and RNA, a uracil-copper catalytic system was developed to promote ring-opening allylation of cyclopropanols with allylic alcohols under water-tolerant conditions. A new C-OH bond-breaking model can well resolve the trade-off between the need for acidic activators for C(allyl)-OH bond cleavage and the demand for strong basic conditions for generating homoenolates. Therefore, Morita-Baylis-Hillman alcohols, rather than their pre-activated versions, could be incorporated directly into dehydrative cross-coupling with cyclopropanols delivering water as the only by-product. A variety of functionalized δ,ε-unsaturated ketones were obtained in good-to-high yield with high E-selectivity.

Chemoselective Intramolecular Morita-Baylis-Hillman Reaction; Acrylamide and Ketone as Sluggish Reacting Partners on a Labile Framework

Chemoselectivity is an important issue frequently encountered while working over labile precursors. Carbonyl compounds with a heteroatom at the β carbon are sensitive precursors because they are prone to elimination under different conditions. Morita-Baylis-Hillman (MBH) reaction, although a widespread method for C-C bond formation, has its own limitations. Acrylamide and ketone are such limitations of the MBH reaction. Using them together for an intramolecular MBH (IMBH) reaction on a labile framework prone to elimination is a significant 2-fold synthetic challenge. A highly chemoselective IMBH reaction on such precursors has been established using 1,4-diazabicyclo[2.2.2]octane (DABCO) as a promoter. The protocol leads to quick access to a diversely substituted and functionalized piperidone framework in high yields. Various substitution patterns in the form of 34 successful examples have been studied. A diastereoselective version and tolerance to various functional and protecting groups are the added advantages of the developed methodology. A tertiary carbon at the β position of ketone, however, led to complete reversal of selectivity and gave only the elimination product. Control experiments toward a better understanding of the substitution pattern, role of catalyst, and mechanistic study have been carried out. As an application of the IMBH adduct, a one-step allylic rearrangement for the dihydropyridone framework has also been demonstrated.

Regioselective and Diastereoselective Construction of Diverse Dispiro-Indanone-Fluorenone-Oxindole Motifs

A convenient synthetic protocol for regioselective and diastereoselective construction of complex dispiro-indanone-fluorenone-oxindole motifs was developed by the base-promoted annulation reaction of bindone and MBH carbonates of isatins by adjusting reaction conditions. DABCO promoted the annulation reaction of bindone and MBH carbonates of isatins in DCM at room temperature, affording dispiro[indene-2,4'-fluorene-1',3″-indoline] derivatives in good yields and with high diastereoselectivity. Triethylamine promoted the annulation reaction of two molecular 1,3-indanediones and MBH esters of isatins in ethanol at elevated temperature and selectively gave dispiro[indene-2,4'-fluorene-3',3″-indolines] in moderate yields. However, triethylamine promoted the annulation reaction of excess 1,3-indanediones and MBH esters of isatins in refluxing ethanol, affording dispiro[indene-2,4'-fluorene-3',3″-indolines] with the Z-isomer as the major product and the E-isomer as the minor product.

Organocatalytic (1+4)-Annulations of MBH Adducts with Electron-Deficient Systems

Benefited from the rapid development of MBH reaction, the reaction of MBH adducts have been established as the most synthetically useful transformations. However, compared with the well-established allylic alkylations and (3+2)-annulations, the (1+4)-annulations of MBH adducts have not developed rapidly until recently. As a helpful complement to the (3+2)-annulations of MBH adducts, the (1+4)-annulations of MBH adducts opens a robust access to structurally diverse five-membered carbo- and heterocycles. This paper summarizes recent advances in organocatalytic (1+4)-annulations using MBH adducts as 1 C-synthons for the construction of functionalized five-membered carbo- and heterocycles.

Phosphine-Catalyzed (3 + 2) Annulation of γ-Substituted Cinnamic Aldehyde-Derived Morita-Baylis-Hillman Carbonates through Remote Activation

A series of γ-substituted Morita-Baylis-Hillman (MBH) carbonates were synthesized and subjected to phosphine-catalyzed annulations with electrophilic exocyclic alkenes, giving various valuable spirocyclopentenes in moderate to excellent yields with moderate to excellent diastereoselectivities. A large scope of MBH carbonates bearing γ-hydrogen, alkenyl, and alkynyl substituents was well tolerated. The annulation unprecedentedly involves β-, γ-, and δ-carbons of MBH carbonates.

Phosphine-Catalyzed Domino Regio- and Stereo-Selective Hexamerization of 2-(Bromomethyl)acrylates to 1,2-Bis(cyclohexenyl)ethenyl Derivatives

A phosphine-catalyzed domino assembly of six units of 2-bromomethyl acrylates afforded polyalkenyl adducts containing two cyclohexenyl rings. This reaction occurs under mild conditions providing the final product by formation of seven carbon-carbon bonds and four stereocenters. Experimental and computational studies support an initial dimerization of the substrate, which in turn trimerizes involving two totally regio- and stereocontrolled Diels-Alder cycloadditions. The yield of the hexamerization of the 2-bromomethyl acrylates depends on the size of the ester function. The protocol has also proved to be practicable on a gram scale.

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.

Fluoroalkylation of Activated Allylic Acetates through Radical-Radical Coupling: Organophotoredox/DABCO Catalytic System

A novel organophotoredox/DABCO catalytic system for the fluoroalkylation of activated allylic acetates via radical-radical coupling is described. The method offers mild reaction conditions, high selectivity, and broad substrate compatibility and enabled diverse bioactive molecules, FDA-approved drugs, and amino acid derivatives to be incorporated into transformation. This study expands the synthetic toolbox for the construction of fluorine-containing molecules.

Highly Regio- and Diastereoselective Phosphine-Catalyzed [2 + 4] Annulation of Benzofuran-Derived Azadienes with Allyl Carbonates: Access to Spiro[benzofuran-cyclohexanes]

A novel highly regio- and diastereoselective phosphine-catalyzed [2 + 4] annulation of benzofuran-derived azadienes (BDAs) with acidic hydrogen-tethered allyl carbonates has been developed ingeniously. A range of functionalized spiro[benzofuran-cyclohexane] derivatives with two consecutive stereocenters were smoothly obtained in moderate to excellent yields under mild reaction conditions from readily available materials. Moreover, this method is a practical and scalable strategy that creates the core structural motif of the fungistatic drug, griseofulvin.

DMAP-Catalyzed [4+3] Spiroannulation of Pyrazolone-Derived Morita-Baylis-Hillman Carbonates with N-(o-Chloromethyl)aryl Amides to Forge Spiro[pyrazolone-azepine] Scaffolds

A novel DMAP-catalyzed [4+3] spiroannulation of pyrazolone-derived Morita-Baylis-Hillman carbonates with N-(o-chloromethyl)aryl amides was developed. This reaction led to the assembly of medicinally relevant pyrazolone and azepine nuclei into a structurally new spirocyclic scaffold, and a diverse array of spiro[pyrazolone-azepine] products were afforded in good to excellent yields (up to 93%) with a wide substrate scope (23 examples) under mild conditions. Moreover, a gram-scale reaction and product transformations were conducted, which further increased the diversity of products.

Lewis-Base-Catalyzed Enantioselective Formal [4 + 2] Annulations of Morita-Baylis-Hillman Carbonates: Access to Tetrahydroquinolines Derivatives

The Lewis-base-catalyzed enantioselective formal [4 + 2] annulation reaction of o-acylamino-aryl MBH carbonates and electron-deficient olefins was developed. Tetrahydroquinolines with three sequential stereogenic centers containing a quaternary stereocenter were obtained in high yields with good enantioselectivity.

DABCO-Catalyzed Mono-/Diallylation of N-Unsubstituted Isatin N,N′-Cyclic Azomethine Imine 1,3-Dipoles with Morita-Baylis-Hillman Carbonates

Allylation of N-unsubstituted isatin N,N′-cyclic azomethine imines with Morita-Baylis-Hillman carbonates in the presence of 1–10 mol% DABCO in DCM at room temperature, rapidly gave N-allylated and N, β-diallylated isatin N,N′-cyclic azomethine imine 1,3-dipoles in moderate to high yields. The reaction features mild reaction conditions, easily practical operation, and short reaction times in most cases. Furthermore, the alkylated products were transformed into novel bicyclic spiropyrrolidine oxoindole derivatives through the [3+2] or [3+3]-cycloaddition with maleimides or Knoevenagel adducts.

Stereo- and Regiospecific SN2' Reaction of MBH Adducts with Isocyanoacetates: en Route to Transition-Metal-Free α-Allylation of Isocyanoacetates

Herein, we report that under mild and transition-metal-free conditions an unprecedented and practical S_N2' reaction of Morita-Baylis-Hillman adducts with isocyanoacetates takes place in a stereo- and regiospecific manner. This reaction which tolerates a wide variety of functionalities delivers transformable α-allylated isocyanoacetates in high efficiencies. Preliminary studies on the asymmetric version of this reaction indicate that ZnEt₂/chiral amino alcohol combinations are an asymmetric catalytic system for this transformation, giving an enantioenriched α-allylated isocyanoacetate with a chiral quaternary carbon in a high yield.

Acyl Transfer-Driven Rauhut-Currier Dimerization of Morita-Baylis-Hillman Ketones

A serendipitous Rauhut-Currier dimerization of 1,1-disubstituted activated olefins derived from Morita-Baylis-Hillman adducts was observed in the presence of DABCO. The reaction is driven by the migration of an acyl group and produces multifunctionalized enol esters in yields greater than 90% in most cases, without necessitating column chromatographic purification. The acyl transfer is thought to proceed via a transition state typical of a Morita-Baylis-Hillman (MBH) reaction, supported by a brief mechanistic study involving computational calculations.

A New MBH Adduct as an Efficient Ligand in the Synthesis of Metallodrugs: Characterization, Geometrical Optimization, XRD, Biological Activities, and Molecular Docking Studies

This article reports the synthesis, characterization, geometrical optimization, and biological studies of new MBH-based organometallic compounds of medicinal significance. The ligand (MNHA) was prepared via the Morita-Baylis-Hillman (MBH) synthetic route, from aromatic aldehyde containing multiple functional groups. Metal complexes were prepared in an alkaline medium and under other suitable reaction conditions. Spectral and elemental analyses were used to identify the structural and molecular formulas of each compound. Optimized geometry was determined through density functional theory (DFT) B3LYP and 6-311++ G (d,p) basis set for the MBH adduct, whereas structures of novel complexes were optimized with the semi-empirical PM6 method. Powder XRD analysis furnished the crystal class of complexes, with Co³⁺, Cr³⁺, and Mn²⁺ being cubic, while Ni²⁺ was hexagonal, and Cu²⁺ was orthorhombic. Moreover, the ligand, along with Ni²⁺ and Co³⁺ complexes, showed profound antibacterial action against S. aureus, E. coli, B. pumilis, and S. typhi. Additionally, all of the complexes were shown to persist in the positive antioxidant potential of the ligand. Contrarily, not a single metal complex conserved the antifungal potentials of the ligand.

Synthesis of 1,3,5-trisubstituted pyrazoles via 1,3-dipolar cycloaddition of nitrile imines with ninhydrin-derived Morita-Baylis-Hillman carbonates

An effective synthetic method for 1,3,5-trisubstituted pyrazoles via 1,3-dipolar cycloaddition reaction has been developed. This reaction could smoothly proceed between ninhydrin-derived Morita-Baylis-Hillman carbonates and nitrilimines to provide a wide scope of differently substituted pyrazoles in high yields (up to 95%). In addition, the reaction mechanism was also proposed to explain its regioselectivity.

Efficient construction of diverse spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] via [3 + 3] cycloaddition of MBH carbonates of isatins with β-enamino maleimides

An efficient method to construct unique spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] was successfully developed via a DABCO promoted formal [3 + 3] cycloaddition reaction of MBH carbonates of isatins with β-enamino maleimides in acetonitrile at room temperature. This reaction afforded multifunctionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] and spiro[dipyrrolo[3,4-b:3',4'-e]pyridine-8,3'-indolines] in good yields and with lower diastereoselectivity. The relative configuration of the two diasteromers of the spiro compounds was clearly elucidated by the determination of eight single crystal structures.

Chemoselective tandem SN2'/SN2''/inter- or intramolecular Diels-Alder reaction of γ-vinyl MBH carbonates with phenols and o-hydroxychalcones

An unprecedented consecutive S_N2'/S_N2'' addition of phenol to γ-vinyl MBH carbonate forms a reactive diene intermediate, followed by a dimerization/elimination process to give functionalized exocyclohexenes with excellent chemoselectivity. When using o-hydroxychalcones as pronucleophiles, an S_N2'/S_N2''/intramolecular Diels-Alder reaction sequence occurs, selectively producing a series of pharmaceutically intriguing tricyclic chromane derivatives with good diastereoselectivity. The good nucleophilicity and fair nucleofugicity exhibited by phenoxy anion play a pivotal role in the S_N2'' addition step.

Synthetic and Computational Study of the Enantioselective [3+2]-Cycloaddition of Chromones with MBH Carbonates

Highly efficient and straightforward access to enantioenriched five-membered ring-fused chromanones is developed via [3+2]-cycloaddition of 3-cyanochromones with Morita-Baylis-Hillman carbonates. Densely functionalized chiral cyclopenta[b]chromanones with three continuous quaternary and tertiary stereogenic carbon centers were obtained in high yields with high ee and dr (≤97% yield, 97% ee, and >20:1 dr). Moreover, density functional theory calculations have been carried out to investigate the mechanism and regio- and diastereoselectivity of the reaction.

Tri(n-butyl)phosphine-promoted domino reaction for the efficient construction of spiro[cyclohexane-1,3'-indolines] and spiro[indoline-3,2'-furan-3',3''-indolines]

The tri(n-butyl)phosphine-catalyzed reaction of isatylidene malononitriles and bis-chalcones in chloroform at 65 °C afforded functionalized spiro[cyclohexane-1,3'-indolines] in good yields and with good diastereoselectivity. On the other hand, the tri(n-butyl)phosphine-catalyzed reaction of 3-(ethoxycarbonylmethylene)oxindoles and bis-chalcones gave functionalized spiro[cyclohexane-1,3'-indolines] with different regioselectivity. Additionally, the tri(n-butyl)phosphine-promoted domino annulation reaction of isatins and ethyl isatylidene cyanoacetates produced spiro[indoline-3,2'-furan-3',3''-indolines] in satisfactory yields.

Synthesis of 2,2-Disubstituted Dihydro-1,4-benzothiazines from Morita-Baylis-Hillman Ketones by an Oxidative Cyclization

An oxidative cyclization ensued upon interaction of Morita-Baylis-Hillman (MBH) ketones with 2-aminothiophenol in the presence of Cs₂CO₃, resulting in the formation of new 2,2-disubstituted dihydro-1,4-benzothiazines. The reaction features an aza-Michael addition and an oxidative cyclization involving the formation of a carbon-sulfur bond and works well over a wide range of MBH ketones to deliver the dihydrobenzothiazines in good yields in reasonable reaction times under mild conditions.

Organocatalytic Enantioselective Formal (4 + 2)-Cycloadditions of Phosphine-Containing Dipoles with Isocyanates

Phosphine-catalyzed enantioselective formal (4 + 2)-cycloadditions of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with isocyanates have been developed for the first time. The initial S_N2' attack of the chiral phosphine organocatalyst on 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates generated the key phosphine-containing dipolar intermediates, and the subsequent formal cycloaddition with isocyanates furnished a broad scope of 3,4-dihydroquinazolin-2-ones in 60-84% yields with 61-92% ee.

Phosphine-Mediated Sequential [2+4]/[2+3] Annulation to Construct Pyrroloquinolines

A domino [2+4]/[2+3] sequential annulation reaction of MBH carbonates with N-unprotected indoles has been developed to provide various pyrroloquinoline derivatives in ≤94% yield and 20:1 dr. The reaction could be either mediated by stoichiometric PCy₃ or catalyzed by R₃PO via P^III/P^V═O redox cycling in the presence of phenylsilane. This method assembles polycyclic 1,7-fused indoles in one step diastereoselectively.

Organocatalytic Regio- and Enantioselective [3 + 2]-Annulations of Ninhydrin-Derived Morita-Baylis-Hillman Carbonates with 3-Methyleneoxindoles

A type of Morita-Baylis-Hillman (MBH) carbonates has been developed from ninhydrin. These MBH carbonates have been successfully employed as 3C-synthons in the organocatalytic asymmetric [3 + 2]-annulations of the isatin-derived electron-deficient olefins, affording structurally diverse spirooxindoles in high yield with excellent stereoselectivity. In particular, the regioselectivity of MBH carbonates was controlled by the reaction partner, 3-methyleneoxindoles with carbonyl groups (R = ArCO), affording β-selective products and 3-methyleneoxindoles with ester groups (R = CO₂Me) furnishing γ-selective products. The representative scale-up reactions and transformation of product were examined. The reaction mechanism was expounded by control experiments.

Phosphine-Catalyzed Dearomative [3 + 2] Cycloaddition of Benzoxazoles with a Cyclopropenone

The triphenylphosphine-catalyzed dearomative [3 + 2] cycloaddition of benzoxazoles with 1,2-diphenylcyclopropenone is herein described. The reaction scope, mechanism, and possible future applications of this rare organocatalyzed cycloaddition are herein discussed.

Catalyst-Controlled Regiodivergent Synthesis of α/β-Dipeptide Derivatives via N-Allylic Alkylation of O-Alkyl Hydroxamates with MBH Carbonates

A controllable and regiodivergent N-allylation reaction involving readily available O-alkyl hydroxamates derived from natural α-amino acids has been developed, allowing regiospecific access to α/β-dipeptides containing α-unsaturated β-amino acids moieties in moderate to good yields. The regioselectivity could be conveniently switched by alternation of the catalysts and solvents.

A formal [4 + 1] cycloaddition reaction of Baylis–Hillman bromides with sulfur ylides: facile access to α-alkenyl lactones

A formal [4 + 1] cycloaddition reaction of Baylis–Hillman adducts with sulfur ylides has been developed for the first time.

Asymmetric [3 + 2] spiroannulation of pyrazolone-derived Morita–Baylis–Hillman carbonates with alkynyl ketones: facile access to spiro[cyclopentadiene-pyrazolone] scaffolds

A tertiary amine-catalyzed asymmetric [3 + 2] spiroannulation reaction of pyrazolone-derived Morita–Baylis–Hillman carbonates with alkynyl ketones was achieved under mild conditions. This protocol offers a facile approach to chiral spiro[cyclopentadiene-pyrazolone]...

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.

Stereoselective Access to Spirooxindoles and Bisoxindoles Through Organocatalyzed Asymmetric Divergent Transformations of Isatin-derived MBH Carbonates

An interesting β-isoquinidine catalyzed divergent reaction was developed to produce either spirocyclopentene oxindoles, spirocyclopentadiene oxindoles or bisoxindoles in a high enantioselective fashion. The utility of this protocol was demonstrated by the versatile transformations of the products. This work not only represents the first highly stereoselective intermolecular catalytic asymmetric allylic alkylation reaction between two isatin-derived MBH carbonate molecules but also constitutes a rare example of isatin-derived MBH carbonate-based enantioselective and α-regioselective [3+2] cycloaddition reactions.

Phosphine-Catalyzed (4 + 2) Annulation of δ-Sulfonamido-Substituted Enones with 1,1-Dicyanoalkenes: Synthesis of Piperidine Derivatives

The δ-sulfonamido-substituted enones were employed as phosphine acceptor in phosphine-catalyzed (4 + 2) annulation of 1,1-dicyanoalkenes. They served as a four-membered synthon to react with 1,1-dicyanoalkenes under mild reaction conditions, producing piperidine derivatives in moderate to excellent yields with good to excellent diastereoselectivities.

Generation of zwitterionic trifluoromethyl N-allylic ylides and their use in switchable divergent annulations

The previously unreported zwitterionic N-allylic ylide species from the corresponding Morita-Baylis-Hillman carbonates of trifluoromethyl ketones and acrylonitrile are generated under the catalysis of cinchona-derived tertiary amines, and subsequently participate in switchable asymmetric [3+2] or [4+1] annulations with 1-azadienes in chemo-, regio-, and stereodivergent manners via catalyst or substrate control. A diverse range of frameworks, having a trifluoromethylated all-carbon quaternary stereogenic centre or a tetrasubstituted alkene moiety, are generally constructed in good yields with excellent enantioselectivity.

DABCO catalyzed [4+2] annulations of Morita-Baylis-Hillman carbonates with isocyanates

A highly concise method for 1,4-diazabicyclo[2.2.2]octane (DABCO) catalyzed [4+2] annulations of o-amino-acylation of aryl MBH carbonates with isocyanates has been developed. For the first time, MBH carbonates served as 1,4-dipoles, providing functionalized 3,4-dihydroquinazolinones in mild conditions with good to excellent yields. The density functional theory calculations of the mechanism supports our hypothesis.