Ylide compounds reactivity properties

The known nonclassical A,B-diheteropentalenes consist of compounds containing an annelated thiophene or selenophene ring, the only uncharged nonradical representations of which contain a tetravalent sulfur or selenium, while the charged structures represent carbonyl, azomethine, thiocarbonyl or selenocarbonyl ylides. The parent systems have not yet been synthesized, only substituted compounds being known. The properties of these substituted derivatives provide a good measure of understanding of the reactivities of the parent systems. 

Phosphoranes or phosphorus ylides are an extremely useful class of compounds in synthetic chemistry. Several recent studies have been published on the preparation, properties, and applications of ylides as reactants or ligands. Also, mechanistic investigations on the reactivity as well as on the antibacterial, antifungal and/or antitumoral activity of such compounds have been detailed. 

---