Iodonium iodides, cyclic

A new method for the synthesis of cyclic iodonium ylides 484 has been developed via Rh2(OAc)4-catalyzed decomposition of a-diazodicarbonyl compounds and intramolecular capture of carbenes by aryl iodides (93MI2). 

The reaction of the cyclic hindered iodonium perchlorate (46) with triphenylphosphine led unexpectedly to the vinyl iodide (75) as the major product, along with the expected vinylphosphonium salt (76). This result was explained by the formation of an iodophosphonium intermediate (77) which follows two different pathways for the ligand coupling process.i (Scheme 5.6)... 

The most important representative of cyclic iodonium salts, the dibenziodolium or diphenyleneiodonium (DPI) cation 238, known in the form of iodide, chloride, hydrosulfate, hexafluorophosphate, or tetrafluoroborate salts, can be obtained by three different procedures (A, B and C) summarized in Scheme 2.71. Method A, originally developed by Mascarelli and Benati in 1909 [355], uses 2,2 -diaminodiphenyl (235) as the starting material, which upon diazotization with sodium nitrite in a hydrochloric acid solution followed by potassium iodide addition, gives DPI 238 as iodide salt. A similar reaction starting from 2-amino-2 -iododiphenyl 236 affords DPI as hexafluorophosphate or tetrafluoroborate in excellent yields (Method B) [356]. The third method involves the peracetic oxidation of 2-iodobiphenyl (237) to an iodine(III) intermediate that then cyclizes in acidic solution (Method C) [357]. More recently, these methods were used to prepare the tritium labeled DPI and of its 4-nitro derivative [358]. 

Methyl vinyl ketone (195) underwent Heck reaction with cyclic iodonium salt 196 in the presence of Pd(OAc)2 and proton sponge to give binaphthyl iodide 197 in 81% yield (Scheme 22.45) [68]. When the base was switched from proton sponge to EtsN, annulated product 198 was produced in 88% yield the conditions smoothly catalyzed not only the intermolecular Heck reaction but also intramolecular Heck reaction of 197. It is noteworthy that 196 is utilized as a synthetic equivalent of 2,2 -diiodobinaphthyl. 

---