Enantioselective [3 + 2] Cycloaddition of Allenes to Acrylates Catalyzed by Dipeptide-Derived Phosphines: Facile Creation of Functionalized Cyclopentenes Containing Quaternary Stereogenic Centers

Synthesis of 3,4-Disubstituted Maleimide Derivatives via Phosphine-Catalyzed Isomerization of α-Succinimide-Substituted Allenoates Cascade γ'-Addition with Aryl Imines

3,4-disubstituted maleimides find wide applications in various pharmacologically active compounds. This study presents a highly effective approach for synthesizing derivatives of 3,4-disubstituted maleimides through the direct isomerization of α-succinimide-substituted allenoates, followed by a cascade γ'-addition and aryl imines using PR3 as a catalyst. The resulting series of 3,4-disubstituted maleimides exhibited excellent stereoselectivities, achieving yields of up to 86%. To our knowledge, the phosphine-mediated γ'-addition reaction of allenoates is seldom reported.

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.

Nickel-Catalyzed Three-Component Tandem Radical Cyclization 1,5-Difunctionalization of 1,3-Enynes and Alkyl Bromide

A nickel-catalyzed three-component tandem radical cyclization reaction of aryl bromides with 1,3-enynes and aryl boric acids to construct γ-lactam-substituted allene derivatives has been described. This protocol provides lactam alkyl radicals through the free radical cyclization process, which can be effectively used to participate in the subsequent multicomponent coupling reaction so that 1,3-enynes could directly convert into corresponding poly-substituted allene compounds. In addition, this efficient method enjoys a broad substrate scope and provides a series of 1,5-difunctionalized allenes in a one-pot reaction.

Phosphine-catalyzed activation of cyclopropenones: a versatile C3 synthon for (3+2) annulations with unsaturated electrophiles

We herein report a phosphine-catalyzed (3 + 2) annulation of cyclopropenones with a wide variety of electrophilic π systems, including aldehydes, ketoesters, imines, isocyanates, and carbodiimides, offering products of butenolides, butyrolactams, maleimides, and iminomaleimides, respectively, in high yields with broad substrate scope. An α-ketenyl phosphorous ylide is validated as the key intermediate, which undergoes preferential catalytic cyclization with aldehydes rather than stoichiometric Wittig olefinations. This phosphine-catalyzed activation of cyclopropenones thus supplies a versatile C3 synthon for formal cycloadditon reactions.

Asymmetric Synthesis of Cyclopentene Compounds Containing All-Carbon Quaternary Stereocenters by (3 + 2) Cycloaddition and Its Application in the Formal Synthesis of (R)-(-)-Puraquinonic Acid

A highly stereoselective (3 + 2) cycloaddition for the asymmetric synthesis of versatile cyclopentene compounds containing all-carbon quaternary stereocenters was developed. The phosphine-catalyzed reactions of alkynoates with α-alkylated electron-deficient alkenes bearing Oppolzer's camphorsultam showed high to excellent diastereoselectivities and perfect regioselectivities. The usefulness of this reaction was demonstrated in the concise formal synthesis of (R)-(-)-puraquinonic acid.

Phosphine-Catalyzed Enantioselective (3+2) Annulation of Vinylcyclopropanes with Imines for the Synthesis of Chiral Pyrrolidines

A phosphine-catalyzed highly enantioselective and diastereoselective (up to 98 % ee and >20 : 1 dr) (3+2) annulation between vinylcyclopropanes and N-tosylaldimines has been developed, which allows facile access to a range of highly functionalized chiral pyrrolidines. Notably, this method makes use of vinylcyclopropanes as a synthon for phosphine-mediated asymmetric annulation reaction, which will offer new opportunities for potential applications of cyclopropanes substrates in phosphine-catalyzed organic transformations.

Phosphine-catalyzed Divergent Domino Processes between γ-Substituted Allenoates and Carbonyl-Activated Alkenes

Highly enantioselective and chemodivergent domino reactions between γ-substituted allenoates and activated alkenes have been developed. In the presence of NUSIOC-Phos, triketone enone substrates smoothly reacted with γ-substituted allenoates to form bicyclic furofurans in good yields with high stereoselectivities. Alternatively, the reaction between diester-activated enone substrates and γ-substituted allenoates formed chiral conjugated 1,3-dienes in good yields with excellent enantioselectivities. Notably, by employing substrates with subtle structural difference, under virtually identical reaction conditions, we were able to access two types of chiral products, which are of biological relevance and synthetic importance.

Highly enantioselective and chemodivergent domino reactions between γ-substituted allenoates and activated alkenes have been developed.

Discovery of Annulating Reagents Enabling the One-Step and Highly Stereoselective Synthesis of Cyclopentyl and Cyclohexyl Cores

The use of the unprecedented annulating reagents methyl N-(tert-butylsulfinyl)-4-chlorobutanimidate and methyl N-(tert-butylsulfinyl)-5-bromopentanimidate enables the diastereoselective preparation of 5- and 6-membered carbocycles bearing three contiguous stereocenters. These synthons undergo cycloaddition with a variety of Michael acceptors to form cyclopentane/cyclohexane rings with excellent stereochemical control, generating only one of the eight possible diastereomers. This novel methodology has enabled the highly enantioselective and high yielding synthesis of novel chemotypes of pharmacological relevance.

Substrate-controlled, PBu3-catalyzed annulation of phenacylmalononitriles with allenoates enables tunable access to cyclopentenes

Divergence in the PBu3-catalyzed [3+2] annulation of phenacylmalononitriles with allenoates, controlled by the γ-substitution on allenoates, offers a tunable synthesis of multifunctionalized cyclopentene carboxamides and cyclopentenols. An unprecedented formation of cyclopentene carboxamide was observed when allenic esters bearing a substitution at the γ-position were employed, while unsubstituted allenoates produced cyclopentenols. The former reaction likely involves a Michael/aldol/nucleophilic cyclization sequence in a domino manner.

Phosphine-Catalyzed Cascade Michael Addition/[4+2] Cycloaddition Reaction of Allenoates and 2-Arylidene-1,3-indanediones

The phosphine-catalyzed cascade Michael addition/[4+2] cycloaddition reaction of tetrahydrobenzofuranone-derived allenoates and 2-arylidene-1,3-indanediones has been reported, affording spirocyclic 1,3-indanedione derivatives in moderate to high yields with moderate to good diastereoselectivities. A scaled-up reaction worked well under mild conditions, and a plausible mechanism is proposed.

Construction of spirooxindole-fused spiropyrazolones containing contiguous three stereogenic centres via [3 + 2] annulation utilizing a ferrocene derived bifunctional phosphine catalyst

Regional and stereoselective construction of spirooxindole-fused spiropyrazolones containing contiguous three stereogenic centres via [3 + 2] annulation catalyzed by ferrocene derived bifunctional phosphine.

Phosphine-catalyzed [3 + 2] annulation of 2-aminoacrylates with allenoates and mechanistic studies

A phosphine catalyzed formal [3 + 2] annulation was disclosed, affording 3-pyrrolines containing an amino quaternary stereogenic center in good to excellent yields. The catalytic mechanism was investigated by DFT and kinetic studies.

Asymmetric synthesis of benzothiazolopyrimidines with high catalytic efficiency and stereoselectivity under bifunctional phosphonium salt systems

Bifunctional phosphonium salt-mediated formal [4+2] annulation towards chiral benzothiazolopyrimidine compounds with excellent yields and stereoselectivities.

Oxidation of Enones for Regioselective [3+2] Cycloaddition through γ-Enone Radical Intermediates

Herein, an oxidization reaction of enones with a Cu^II complex that leads to a new type of regioselective [3+2] cycloaddition is reported. Highly functionalized cyclopentenes and spirocyclic compounds are obtained in moderate-to-good yields. This cycloaddition reaction occurred through the formation of γ-enone radicals, providing a rarely explored reactivity pattern for enones.

Highly Regio- and Enantioselective Dienylation of p-Quinone Methides Enabled by an Organocatalyzed Isomerization/Addition Cascade of Allenoates

A novel catalytic asymmetric dienylation of para-quinone methides with allenoates has been developed. Under mild conditions catalyzed by ( R)-SITCP, various dienylated bisarylmethides were obtained in moderate to good yields (up to 82% yield) and excellent enantioselectivities (90-98% ees). The efficacy and robustness were demonstrated by 27 examples of chiral dienylation products. A plausible mechanism, which involved 1,2 H-shift and umpolung of allenoates, was proposed based on deuterium labeling experiments and previous reports.

Direct access to spirobiisoxazoline via the double 1,3-dipolar cycloaddition of nitrile oxide with allenoate

The double [3 + 2]-cycloadditions between nitrile oxides and allenoates have been achieved. In the presence of DABCO combined with Et₃N, 2-substituted buta-2,3-dienoates reacted with oxime chlorides to afford spirobiisoxazolines in 55-90% yields via the double 1,3-dipolar cycloaddition. Notably, the construction of double isoxazoline moieties and two chiral centers including a spiro carbon center was achieved.

Organocatalysts Derived from Unnatural α-Amino Acids: Scope and Applications

The organocatalytic properties of unnatural α-amino acids are reviewed. Post-translational derivatives of natural α-amino acids include 4-hydroxy-l-proline and 4-amino-l-proline scaffolds, and also proline homologues. The activity of synthetic unnatural α-amino acid-based organocatalysts, such as β-alkyl alanines, alanine-based phosphines, and tert-leucine derivatives, are reviewed herein. The organocatalytic properties of unnatural monocyclic, bicyclic, and tricyclic proline derivatives are also reviewed. Several families of these organocatalysts permit the efficient and stereoselective synthesis of complex natural products. Most of the reviewed organocatalysts accelerate the reported reactions through covalent interactions that raise the HOMO (enamine intermediates) or lower the LUMO (iminium intermediates).

A novel chiral DMAP–thiourea bifunctional catalyst catalyzed enantioselective Steglich and Black rearrangement reactions

A novel chiral DMAP–thiourea bifunctional catalyst has been prepared and applied in the highly enantioselective Steglich and Black rearrangement reactions.

Creation of bispiro[pyrazolone-3,3′-oxindoles] via a phosphine-catalyzed enantioselective [3 + 2] annulation of the Morita–Baylis–Hillman carbonates with pyrazoloneyldiene oxindoles

A [3 + 2] annulation between the Morita–Baylis–Hillman (MBH) carbonates and pyrazoloneyldiene oxindoles catalyzed by (S)-SITCP has been developed.

Phosphine-catalyzed regiodivergent annulations of γ-substituted allenoates with conjugated dienes

A phosphine catalyzed regiodivergent annulation of γ-substituted allenoates with conjugated dienes is reported. The high regioselectivity can be achieved by tuning the nucleophilicity of the phosphine catalyst.

Phosphine Organocatalysis

The hallmark of nucleophilic phosphine catalysis is the initial nucleophilic addition of a phosphine to an electrophilic starting material, producing a reactive zwitterionic intermediate, generally under mild conditions. In this Review, we classify nucleophilic phosphine catalysis reactions in terms of their electrophilic components. In the majority of cases, these electrophiles possess carbon-carbon multiple bonds: alkenes (section 2), allenes (section 3), alkynes (section 4), and Morita-Baylis-Hillman (MBH) alcohol derivatives (MBHADs; section 5). Within each of these sections, the reactions are compiled based on the nature of the second starting material-nucleophiles, dinucleophiles, electrophiles, and electrophile-nucleophiles. Nucleophilic phosphine catalysis reactions that occur via the initial addition to starting materials that do not possess carbon-carbon multiple bonds are collated in section 6. Although not catalytic in the phosphine, the formation of ylides through the nucleophilic addition of phosphines to carbon-carbon multiple bond-containing compounds is intimately related to the catalysis and is discussed in section 7. Finally, section 8 compiles miscellaneous topics, including annulations of the Hüisgen zwitterion, phosphine-mediated reductions, iminophosphorane organocatalysis, and catalytic variants of classical phosphine oxide-generating reactions.

Toward a Predictive Understanding of Phosphine-Catalyzed [3 + 2] Annulation of Allenoates with Acrylate or Imine

Both theoretical and experimental studies were performed to explore the mechanism, regioselectivity, and enantioselectivity of phosphine-catalyzed [3 + 2] annulation between allenoates and acrylate or imine. Using density functional theory computations, we predicted that the enantioselective determining step is the nucleophilic addition of acrylate or imine to the catalyst-activated allenoate. In the key step, we proposed two hydrogen bonding interaction models (intermolecular H-bond model and intramolecular H-bond model). For acrylate substrates, the reaction proceeds via the intramolecular H-bond model and the strong noncovalent interactions between the 2-naphthyl ester moiety lead to the re-face attack pathway being more favorable. For imine substrates, the intermolecular H-bond model operates. In the annulation process, the bulky n-propyl oriented toward a crowded, sterically demanding environment plays a significant role in asymmetric induction. The theoretical calculation results agreed with experimental observations, and these results provide valuable insight into catalyst design and understanding of mechanisms of related reactions.