Recent advances in the application of ylide-like species in [4+1]-annulation reactions: an updated review

In this review, the advances made over the last 6 years in [4 + 1]-annulation reactions involving sulfonium, sulfoxonium and ammonium ylides, as well as diazo compounds and carbenes are summarized. The newly emerged methods for generating A(4)-synthons, such as radical, transition metal-catalyzed and photo-redox processes, are outlined. A specific focus is given on the progress in asymmetric [4 + 1]-annulations using organocatalysis and chiral ammonium ylides.