Ylide compounds structural 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. 

Synthesis and Characterisation of Phosphonium Ylides. - We start this section with a phosphanylidene-o -phosphorane (14) which, although not strictly an ylide, has a P-P bond which displays many of the properties of more conventional phosphonium ylides. A crystal structure of (14) revealed a P-P bond length of 2.084(2) A, which is similar to those found in other phos-phanylidene-o( -phosphoranes and is certainly shorter than a typical P-P single bond ca. 2.22 A), indicative of multiple bond character. Compound (14) undergoes reactions with electrophiles (Scheme 1) which demonstrate its nucleophilic... 

It was suggested in 1958 that the minor product obtained from the reaction of dimethylsulfoxonium methylide with benzonitrile possessed the structure 35a. Recently, related compounds 35b and 35c have been prepared by the reaction of the ylide with the cyanamide derivatives 36a and 36b.The structures of the thiazine oxides 35 were assigned on the basis of their spectroscopic properties (Section III,D) in the case of the compound 35a,... 

A summary of the biological properties of iodonium salts has been provided in a 1996 review [1]. Among the numerous known structural types of polyvalent organic iodine compounds, only aryl- and heteroaryliodonium salts and iodonium ylides have considerable, practically useful biological activity. Table 7.1 provides a brief description of the specific biological activity of several patented iodonium derivatives. 

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