Vinyliodonium triflates

A very general and mild procedure for the stereospecific synthesis of aIkenyl(aryl)iodonium triflates 309 involves aryl(cyano)iodonium triflates 308 as iodonium transfer reagents in reactions with stannylated alkenes 307 (Scheme 2.89) [367,443,444], This method was also applied to the preparation of the parent vinyliodonium triflate from tributyl(vinyl)tin [445],... 

The highly strained bicyclo[2.2.1]hept-2-en-5-yne (80) has been formed by reaction of cyclic vinyliodonium triflate (79) with BU4NF in the presence of tetraphenyl-cyclopentadienone, as evidenced by the isolation of cycloadducts (81) and an isomer (83) of cycloadduct (82). ° The total strain energy for (80) is estimated to be 96.7 kcal moP ... 

Diels-Alder reactions of alkynyl(phenyl)iodonium triflates (i.e. containing electron-withdrawing groups in the alkynyl moiety) and [bis(phenyliodonium)] ethyne ditrifiate have been employed for the synthesis of cyclic vinyliodonium salts (equations 143 and 144)17,41. The availability of such compounds offers considerable potential for the elaboration of densely functionalized cyclic molecules. 

The synthetic potential of coupling reactions between vinyliodonium salts and organocuprates has not been exploited. However, some indication of their promise is provided by reported syntheses of bicyclic enediynes in the norbornadiene and 7-oxanor-bornadiene series from the appropriate bisiodonium triflates and lithium dialkynyl-cuprates (equation 221)148. 

Palladium(II)-copper(I) cocatalyzed couplings of several (/ ,/ -dialkylvinyl)phenyliodo-nium triflates with 4-isopropoxy-3-tri- -butylstannyl-3-cyclobutene-l,2-dione (71) in DMF at room temperature have recently been described (equation 259)157. As observed in earlier studies of Cu(I)- or Pd(II)-promoted reactions of vinyliodonium salts, the vinyl ligands are introduced with retention of configuration. Since iodobenzene is a byproduct of ligand coupling, the production of 3-phenyl-4-isopropoxy-3-cyclobutene-1,2-dione might also be expected. However, the (/ ,/ -dialkylvinyl)iodonium ions are much more reactive... 

A similar approach to aryl- and heteroaryl(phenyl)iodonium triflates 285 involves the ligand-transfer reaction between vinyliodonium salt 284 with aryllithiums (Scheme 2.83) [405]. Likewise, the reaction of ( )-[(3-(trifluoromethanesulfonyloxy)ethenyl](aryl)iodonium triflates 286 with aryllithiums or alkynyllithiums can be used for a selective preparation of the respective diaryl- or alkynyl(aryl)iodonium triflates in high yields [406]. 

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