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The mechanism of the phosphine-catalysed domino sequence of alkynoates and activated methylenes has been computationally studied. The computational results revealed that the [3 + 2] annulation sequence could be ruled out, due to a difficult Knoevenagel condensation of aromatic aldehydes and active methylenes. The reaction proceeds through a [4 + 1] annulation pathway, which involves a phosphine-catalysed MBH-type reaction followed by a [1,5]-proton shift and dehydration to afford vinyl phosphonium intermediates as four-carbon synthons in the annulation reaction. Then 1,3-dicarbonyls act as nucleophiles to attack vinyl phosphonium intermediates, subsequently leading to a stepwise [1,3]-proton shift and an intramolecular nucleophilic attack to close the five-member ring.

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.

Nitro compounds are a predominant class of synthetic intermediates and building blocks for the preparation of a wide range of nitrogen-containing compounds in the chemical industry. As such, impressive progress has been currently made in the nitration of aromatics and olefins with excellent functional group tolerance and site-selectivity. In this mini review, we intend to highlight the regiospecific nitration of arenes and alkenes in various reaction systems. The involved mechanisms are discussed as well.

Chromanone is a privileged structure with a wide range of unique biological activities. A phosphine-promoted, three-component domino sequence of salicylaldehyde with but-3-yn-2-one was well designed for the construction of the chromanone skeleton under mild conditions. As a consequence, a series of novel chromanone analogues bearing an all-carbon quaternary center were facilely assembled from commercially available starting materials with moderate to good yields, which hold promising applications in pharmacological studies. Mechanistic experiments were conducted to confirm the proposed mechanism.

A new strategy for the synthesis of functionalized tetrahydrofuran derivatives was developed via a phosphine-catalysed [3 + 2] cyclization reaction of aromatic aldehydes with 4-phenylbut-3-yn-2-one. This is the first example of intermolecular cyclization of ynones with benzaldehydes, which essentially benefited from the intramolecular hydrogen bonding. This new protocol features a broad substrate scope, mild reaction conditions, operational simplicity and easy scale-up.

A diversity-driven three-component 1,3-dipolar cycloaddition of isatins, amino acids and isatin-derived ketimines was developed to facilely assemble dispirooxindole-imidazolidine skeletons bearing vicinal quaternary carbon centers. This protocol features additive-free, minimal solvent usage (0.1 mL DMSO/0.2 mmol scale), wide substrate scope (34 examples), mild reaction conditions (room temperature) and high chemical yield (up to 99%).