Phosphine-Catalyzed [3 + 2] Annulation of 2-Hydroxy-1,4-naphthaquinones and Allenoate: An Allene–Alkene [3 + 2] Annulation Mechanism Involving Consecutive γ-Addition–Aldol Reaction

Broad-Scope (3 + 2) Cycloaddition of Cyclopropanes and Alkynes Enabled by Boronyl Radical Catalysis

Cyclopentene skeletons are ubiquitous in natural products and small molecule drugs. The (3 + 2) cycloaddition of cyclopropanes and alkynes represents an efficient and atom-economic strategy for synthesizing these structures. However, the types of substituents on cyclopropane and alkyne used in previous works show evident limitations, restricting the application of this type of reaction to some extent. Herein, we report a broad-scope (3 + 2) cycloaddition of cyclopropanes and alkynes catalyzed by boronyl radicals. In this method, various substrates, such as mono-, di-, tri-, and tetrasubstituted cyclopropanes, as well as mono- and disubstituted alkynes, were compatible with up to 98% isolated yield.

[3+2] regioselective annulation reaction of 2-arylidene-1,3-indandiones towards synthesis of spirocyclopentenes: understanding the mechanism of γ-attack vs. α-attack using DFT studies

A regioselective [3+2] cyclisation reaction between 2-arylidene-1,3-indanedione and ethyl 2,3-butadienoate catalysed by triphenylphosphine has been demonstrated to synthesize functionalised spirocyclic cyclopentenes. The reaction tolerated various electron-rich and electron-deficient aryl substituted 2-arylidene-1,3-indanediones with high to excellent chemical yields (up to 99%) and moderate to good regioselectivity (up to 5 : 1). DFT studies have also been carried out to understand the regioselective nature of this reaction. The results of Frontier molecular orbital calculations and the activation energy (E a) favour the formation of compound 3avia γ-attack compared to that of 4avia α-attack.

A phosphine-catalysed one-pot domino sequence to access cyclopentene-fused coumarins

A novel phosphine-catalysed, one-pot domino approach for the annulation of 2-formylphenyl alkynoates with activated methylene compounds to construct various cyclopentene-fused dihydrocoumarins is reported. This developed strategy provides a facile and efficient approach for the synthesis of structurally complex coumarins from inexpensive and readily available alkynoates.

Base-Mediated Intramolecular Cyclization of α-Nitroethylallenic Esters as a Synthetic Route to 5-Hydroxy-3-pyrrolin-2-ones

An unprecedented Cs₂CO₃-mediated intramolecular cyclization/rearrangement cascade that transforms α-nitroethylallenic esters to functionalized pyrrolin-2-ones has been uncovered. This reaction provides a new and practical approach for the synthesis of medicinally privileged 5-hydroxy-3-pyrrolin-2-ones under mild conditions. The broad potential of this new method was demonstrated by an efficient Au/Ag-catalyzed heteroarylation of 5-hydroxy-3-pyrrolin-2-ones employing electron-rich heteroarenes to furnish heteroaryl-lactam derivatives.

Phosphine catalyzed [3+2] cyclization/Michael addition of allenoate with CS2 to form 2-thineyl vinyl sulfide

We have developed a DPPE-catalyzed three molecular two component tandem reaction of γ-substituted allenoate and CS2 to construct 2-thineyl vinyl sulfide through phosphine catalyzed [3+2] cyclization followed by Michael addition. The synthetic value of the 2-thineyl vinyl sulfide was demonstrated by a concise synthesis of an anti-glaucoma agent.

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 [3 + 2] cycloadditions of trifluoromethyl enynes/enediynes with allenoates: access to cyclopentenes containing a CF3-substituted quaternary carbon center

The first use of trifluoromethyl-substituted enynes/enediynes as non-classical electron-deficient olefins for phosphine-catalyzed [3 + 2] cycloaddition with allenoates is presented.

Recent advances in phosphine catalysis involving γ-substituted allenoates

This feature article will describe the selected examples of organophosphine catalysis of γ-substituent allenoates with a wide range of electrophiles to give diverse annulations.

Phosphine-Promoted [4 + 3] Annulation of Allenoate with Aziridines for Synthesis of Tetrahydroazepines: Phosphine-Dependent [3 + 3] and [4 + 3] Pathways

In this manuscript, phosphine-dependent [3 + 3] and [4 + 3] annulation reactions of allenoate with aziridines were disclosed. The alkyldiphenylphosphine-promoted [4 + 3] annulation of allenoate with aziridines has been achieved under mild conditions, providing biologically interesting functionalized tetrahydroazepines in moderate to excellent yield with moderate to excellent regioselectivity and diastereoselectivity.

Mechanisms of phosphine-catalyzed [3+3] cycloaddition of ynones and azomethine imines: a DFT study

Mechanisms of PPh₃-catalyzed [3+3] cycloaddition between a ynone and an azomethine imine.

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.

Additive-free regio- and diastereoselective construction of fully-substituted isoxazolidines employing diazo compounds

An efficient additive-free three-component access to densely functionalized isoxazolidines using diazo compounds, nitrosoarene, and allenic esters has been uncovered.

Phosphine-catalyzed dearomative (3 + 2) annulation of 2-nitrobenzofurans and nitrobenzothiophenes with allenoates

An efficient Ph₂PMe-catalyzed dearomative (3 + 2) annulation of 2-nitrobenzofurans, 2-nitrobenzothiophenes, and 3-nitrobenzothiophenes with allenoates is reported.