Iodonium ylides transylidation reactions

In some ylides photolytic conditions were necessary for their transylidation [30]. The conversion of iodonium ylides into a-halogeno derivatives of the parent carbonyl compound (or other precursor) with hydrogen halides is normally effected directly, without isolation of their iodonium salts. A similar reaction with halogens leads to the formation of a,a-bis halogenated products [31]. The reaction of pyridines with the non-isolable PhI=C(CN)2 is of interest, since it permits the ready transfer of the C(CN)2 functionality to the nitrogen of pyridine, quinoline, etc. the yields here were generally moderate but in some cases the products could not be obtained using other dicyanocarbene precursors [32],... 

The thermal reaction, catalysed by Cu(acac)2, of thiobenzophenones with ylides coming from bis arylsulphonyl methane is also likely to proceed by an initial transylidation the main products are here benzo[c]thiophenes [35,36], The car-banionic carbon of iodonium ylides is devoid of nucleophilic character, yet PhI=C(S02Ph)2 gave, with iodomethane, the methylated iododisulphone MeC(I)(S02Ph)2 (68%). This reaction, performed at room temperature without any catalyst, is probably the result of a nucleophilic attack from iodine of iodomethane to iodine of the ylide [37]. 

Whereas iodine-carbon ylides undergo the transylidation reaction normally with copper catalysis, 1,4-dipoles require acid catalysis in this way they react with several nucleophiles through their protonated form, i.e. as iodonium salts, some of which are isolable. Pyridine, nicotinamide, isoquinoline, dimethylsulphide, thiolane... 

Ochiai and coworkers developed a new synthetic approach to various iodonium ylides 429 by the inter-molecular transylidation reactions between halonium ylides under thermal or catalytic conditions (Scheme 2.125) [566,567], The transylidations of bromonium 428 to iodonium 429 ylides proceed under thermal... 

A particularly useful reagent in these carbenoid reactions is the highly soluble and reactive iodonium ylide 780 derived from malonate methyl ester and bearing an ortfw methoxy substituent on the phenyl ring [1059]. This reagent shows higher reactivity than common phenyliodonium ylides in the Rh-catalyzed cyclopropanation, C-H insertion and transylidation reactions under homogeneous conditions. Scheme 3.307 shows representative examples of the carbenoid reactions of ylide 780 [1059]. 

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See also in sourсe #XX -- [ ]

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