Over the past two decades, the rapid development of nucleophilic phosphane catalysis has transported phosphorus ylide chemistry into an area beyond olefination. Phosphorus ylides generated in situ on nucleophilic addition of phosphanes to electrophilic unsaturated species, followed by some necessary proton-transfer steps, have effected many powerful annulation reactions to construct carbo- and heterocycles with multifarious molecular architectures under mild conditions from readily available starting materials. By judicious choice of the nucleophilic phosphanes, efficient ylide annulation reactions with good control over reaction selectivity can be achieved. In this microreview, recent advances in annulation reactions initiated by phosphorus ylides generated in situ are summarized according to the sources of the phosphorus ylides.

An unusual formal [1+4] annulation of α-dicarbonyl compounds with 1,1-dicyano-1,3-dienes has been realized, leading to facile syntheses of cyclopentenimines and cyclopentenones in a unique manner. Mechanistic investigation implies that this reaction takes place through a P(NMe₂)₃-mediated cyclopropanation followed by a base-catalyzed cyclopropane rearrangement. It therefore represents an unprecedented [1+4] annulation mode involving Kukhtin–Ramirez adducts.