Ylides iodonium, conversion

Oxidative methanolysis of azetidinone 176 followed by hydrogenolysis of compound 177 afforded /3-lactam 178, which was protected to obtain the protected amine 179. The best conditions for rearrangement of 179 were found using TFA. Conversion of compound 180 to carbacephem 183 was accomplished by ketone reduction, alcohol protection, and elimination of methanol. Synthesis of carbacephem derivative 186 has been performed by rhodium(n)-catalyzed cycliza-tion of iodonium ylide 185 <1997TL6981> (Scheme 33). The iodonium ylide 185 was easily prepared from the corresponding /3-keto ester 184 and [(diacetoxy)iodo]benzene in good yield. 

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],... 

A method which is related to the conversion of diazo compounds into arsonium ylides is the thermal decomposition of iodonium ylides in the presence of triphenylarsine, either by melting them together " or heating them in solution in the presence of a copper derivative, e.g. equation 29. 

Treatment of iodonium tetrafluoroborates 792 with triethylamine in methanol in the presence of triph-enylphosphine and aldehydes results in Wittig oleflnation to give products 793 (Scheme 3.313), which involves the intermediacy of monocarbonyl iodonium ylides 788 and their subsequent conversion into the respective phosphonium ylides upon the in situ reaction with PhsP [1089]. 

There is evidence, however, that these reactions may not involve conversion of the iodonium ylide into a carbene which then adds to the relevant substrate, but that this substrate is involved prior to cleavage of the carbon-iodine bond [136]. Other ylide interchange reactions which have been recorded include the conversions of various ylides into an oxosulphonium ylide by reaction with sulphur monoxide, generated in situ [141] ... 

Another use of iodonium ylides is as a synthetic route to heterocyclic compounds (Scheme 9). lodonium ylides can be photochemically converted to oxathiole-2-thiones in the presence of CSj. In the presence of phenyl isothiocyanate or styrenes, the iodonium ylides undergo photochemical conversion to 2-phenyliminooxathioles, dihydrofurans, and dihydrobenzofurans, respectively. Many other interesting reactions of iodonium ylides based on the photochemical approach are also reported in the literature. 

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