Catalytic rearrangements of onium ylides in aromatic systems

Onium ylides are reactive intermediates that undergo versatile chemical transformations to give structurally interesting compounds. Rearrangement reactions of onium ylides are of great importance to synthetic organic chemists, as they provide efficient methods for C-C bond formations as well as installation of new stereogenic centers in molecules. Traditionally, onium ylides have been shown to undergo two types of rearrangements, namely, [2,3]- and [1,2]-rearrangements. In recent years, there have been tremendous developments in the field of metal-catalyzed onium ylide rearrangements through catalytic generation of ylide intermediates from diazocompounds. Several examples of selective catalytic onium ylide rearrangements involving sulfonium, oxonium, ammonium, as well as iodonium ylides have been developed over the years especially in allylic and propargylic systems. However, when the π-system that takes part in the rearrangement is part of an aromatic ring, the selectivity for rearrangements of reactive onium ylides is more challenging. In this review, we discuss recent advances in catalyst control of onium ylide rearrangements of aromatic systems.