Phosphine-Mediated Domino Benzannulation Strategy for the Construction of Highly Functionalized Multiaryl Skeletons

Atroposelective Arene-Forming Wittig Reaction by Phosphorus PIII/PV=O Redox Catalysis

The Wittig reaction is renowned as exceptionally versatile method for converting a diversity of aldehydes and ketones into alkenes. Recently, strategies for chiral phosphine catalysis under PIII/PV=O redox cycling emerged to render this venerable transformation stereoselective. Herein, we describe that phosphine redox catalysis enables the enantioselective synthesis of pertinent biaryl atropisomers by means of a stereocontrolled arene-forming Wittig reaction. Key to the process is the release of an endogenous base from readily accessible tert-butyloxycarbonylated Morita-Baylis-Hillman adducts triggered by catalyst intramolecularization, permitting mild phosphine redox catalysis for atroposelective Wittig reactions. By this strategy, a broad diversity of biaryl atropisomers is obtained with up to 94 : 6 enantioselectivity.

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.

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.

A Formal (4 + 2) Cycloaddition of Phosphorus Ylides: Synthesis of Aromatic and Heteroaromatic 1,2-Diesters and Diones

Heteroarylmethylenephosphorus ylides underwent Michael addition with alkynediones and alkynediesters, followed by intramolecular cyclization and elimination of triphenylphosphine oxide to afford 1,2-diaroylbenzenes and 1,2-alkoxycarbonylcarbo- and heterocycles. The analogous (4 + 2) cycloaddition led to the formation of 2,3-diaroylquinolines.

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.

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.

Catalyst-Controlled Divergent Intramolecular Cyclizations of Morita-Baylis-Hillman Carbonates

Unprecedented catalyst-controlled divergent cyclizations of Morita-Baylis-Hillman carbonates have been established using either Cs₂CO₃ or quinuclidine as the catalyst. 1,2-Dihydroquinolines and 4H-3,1-benzoxazines were efficiently synthesized via S_N2' and S_N2'-S_N2' processes, respectively. DFT calculations have led to a deeper understanding of these reaction modes and chemoselectivity.

Designing and Accurately Developing a [6 + 2] Dipolar Cycloaddition for the Synthesis of Benzodiazocines

1,6-Dipolar cycloadditions represent a valuable strategy for the rapid construction of medium-sized rings. Herein, we describe the concept for the design of 1,6-dipoles that bypasses the regioselectivity. Through the introduction of an amino group into Morita-Baylis-Hillman (MBH) carbonates, unprecedented [6 + 2] dipolar cycloadditions were accurately developed with Cs₂CO₃, efficiently delivering a series of benzodiazocines in mild conditions. Computational studies bring a deeper understanding of this reaction.

Design and organocatalytic synthesis of spirooxindole–cyclopentene–isoxazole hybrids as novel MDM2–p53 inhibitors

An organocatalytic 1,6-cycloaddition with exclusive α-regioselectivity to synthesize designed spirooxindole–cyclopentene–isoxazole hybrids as novel MDM2–p53 inhibitors.

Phosphine-Catalyzed Sequential [3+3]/Aza-6π-Electrocyclization Reaction of Cross-Conjugated Azatrienes and δ-Sulfonamido-Allenoates

An unprecedented sequential [3+3]/aza-6π-electrocyclization between cross-conjugated azatrienes and δ-sulfonamido-allenoates, catalyzed by phosphine, has been developed, which provides efficient and facile access to highly functionalized tetrahydroisoquinoline derivatives. The products can be easily transformed into (dihydro)isoquinolines and their fused polycyclic compounds. The reactivity of both azatrienes and δ-sulfonamido-allenoates in this text, acting as a five-atom unit, is unique in the phosphine-catalyzed annulations of allenoates.

Multicomponent benzannulation of allylic P-ylides with isocyanates or aldehydes for construction of anilines and biaryls

The reactivity of allylic phosphorus ylides generated in situ from alkoxycarbonylmethylenephosphoranes and propiolates is investigated toward isocyanates and aromatic aldehydes, which leads to one-pot multicomponent benzannulations for efficient synthesis of polysubstituted anilines and biaryls, respectively. The mechanism may involve a tandem [2+2] cycloaddition/fragmentation/Wittig/cyclization/elimination/aromatization sequence.

Base-Mediated Cyclopentannulation of Ynones with Amino Crotonates for Regio- and Stereoselective Synthesis of Pentafulvenes and Cyclopenta[c]quinolines

A regio- and stereoselective synthesis of unsymmetrically substituted pentafulvenes is reported via the condensation of readily available ynones and amino crotonates under very mild conditions. The mechanism of this 3 + 2 annulation involved a vinylogous Michael addition followed by an intramolecular enamine aldol condensation. Substrates with o-bromo tether further cyclized to pentannulated hydroquinolines through an isomerization/S_NAr in the same reaction pot at the elevated temperature.

Synthetic and mechanistic aspects of sulfonyl migrations

Sulfonyl migrations, frequently described as ‘unusual’ or ‘unexpected’, from the last 20 years, including 1,2-, 1,3-, 1,4-, 1,5-, 1,6- and 1,7-sulfonyl shifts, through either radical or polar processes, either inter- or intramolecularly are reviewed.

Direct access to multi-functionalized benzenes via [4 + 2] annulation of α-cyano-β-methylenones and α,β-unsaturated aldehydes

An efficient [4 + 2] benzannulation of α-cyano-β-methylenones and α,β-unsaturated aldehydes was achieved under metal-free reaction conditions selectively delivering a wide range of polyfunctional benzenes in high yields respectively (up to 94% yield).

An efficient [4 + 2] benzannulation of α-cyano-β-methylenones and α,β-unsaturated aldehydes was achieved under metal-free reaction conditions selectively delivering a wide range of polyfunctional benzenes in high yields respectively (up to 94% yield).

Facile synthesis of biarylmethanes and tetrasubstituted arenes via a base-mediated [3 + 3] benzannulation reaction of Morita–Baylis–Hillman adducts and unsaturated sulfones

A regioselective DBU-mediated [3 + 3] benzannulation reaction of 1,3-bis-sulfonyl propenes and Morita–Baylis–Hillman (MBH) bromides to afford bis-sulfonyl biarylmethanes/arenes is described.

Amine-catalyzed and functional group-controlled chemo- and regioselective synthesis of multi-functionalized CF3-benzene via a metal-free process

A novel strategy for the synthesis of CF₃-containing multi-substituted benzenes with high chemo- and regioselectivities under metal-free and air-tolerant conditions was established.

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.

Phosphine-mediated enantioselective [1 + 4]-annulation of Morita–Baylis–Hillman carbonates with 2-enoylpyridines

This work describes a phosphine-catalyzed asymmetric [1 + 4] annulation of Morita–Baylis–Hillman carbonates with 2-enoylpyridines for constructing the enantiomerically enriched 2,3-dihydrofuran motif. In the presence of (−)-1,2-bis[(2R,5R)-2,5-dimethylphospholano]benzene, a series of Morita–Baylis–Hillman carbonates reacted with 2-enoylpyridines smoothly to afford a wide range of optically active 2,3-dihydrofurans featuring pyridine motifs in high yields with excellent asymmetric induction.

This work describes a phosphine-catalyzed asymmetric [1 + 4] annulation of Morita–Baylis–Hillman carbonates with 2-enoylpyridines for constructing the enantiomerically enriched 2,3-dihydrofuran motif.

Facile synthesis of substituted diaryl sulfones via a [3 + 3] benzannulation strategy

A metal-free and efficient synthesis of highly substituted diaryl sulfones via a base-mediated [3 + 3] benzannulation strategy.

Effective and diastereoselective preparation of dispiro[cyclopent-3′-ene]bisoxindoles via novel [3 + 2] annulation of isoindigos and MBH carbonates

Efficient, one-step preparation of highly steric dispiro[cyclopent-3′-ene]bisoxindoles with two all-carbon quaternary spirocenters and three adjacent cycles in excellent yields and diastereoselectivities under mild conditions.

A phosphine mediated sequential annulation process of 2-tosylaminochalcones with MBH carbonates to construct functionalized aza-benzobicyclo[4.3.0] derivatives

A novel phosphine mediated sequential annulation process to construct functionalized aza-benzobicyclo[4.3.0] derivatives has been developed involving a one-pot process.

Phosphine-catalyzed highly enantioselective [3 + 3] cycloaddition of Morita-Baylis-Hillman carbonates with C,N-cyclic azomethine imines

The first phosphine-catalyzed highly enantioselective [3 + 3] cycloaddition of Morita-Baylis-Hillman carbonates with C,N-cyclic azomethine imines is described. Using a spirocyclic chiral phosphine as the catalyst, a novel class of pharmaceutically interesting 4,6,7,11b-tetrahydro-1H-pyridazino[6,1-a]iso-quinoline derivatives were obtained in high yields with good to excellent diastereoselectivities and extremely excellent enantioselectivities (98->99% ee).

(n)Bu3P-catalyzed desulfonylative [3 + 2] cycloadditions of allylic carbonates with arylazosulfones to pyrazole derivatives

Highly efficient (n)Bu3P-catalyzed desulfonylative [3 + 2] cycloadditions of allylic carbonates with arylazosulfones were developed for the synthesis of pyrazole derivatives. The reactions proceed smoothly under mild conditions to generate corresponding annulation products in good to excellent yields.