Iodonium transfer agent

The best and most versatile contemporary method [22] of preparation of alkynyl(aryl)io-donium salts employs readily available alkynylstannanes [23], and the easily prepared [24] cyano(phenyl)iodonium triflate 7 as an iodonium transfer agent in dichloromethane at low temperatures [Eq. (3)]. This procedure provides excellent yields of iodonium triflates 10 and is applicable to a very broad range of alkynylstannanes, including those with strongly electron-withdrawing groups as summarized in Scheme 3-1. Particularly noteworthy and valuable are the P-keto- and P-amido-substituted species 11 and the cyano-functionalized molecule 11 (Y=CN) [25, 26]. 

The most versatile method of preparation uses the readily available alkynylstannanes (21) and the mixed phenyliodonium triflate (22) as the iodonium transfer agent (equation 7). This procedure works very well for the synthesis of a wide variety of hydrocarbon as well as jS-functionalized alkynyl(phenyl)iodonium trifiates [23 Y=CN, Cl, RC(0), (CH3)2NC(0), ArSOi, etc.]. 

Thienyl(phenyl)iodonium salts and other heteroaryl(phenyl)iodonium salts can be used as the selective heteroaryl transfer agents in reactions with phenol ethers. These heteroarylations occur at room temperature in the hexafluoroisopropanol solution in the presence of trimethylsilyl triflate via a SET mechanism [876]. 

These iodonium ylides function as carbene and nitrene transfer agents. Carbene transfer typically requires a transition-metal catalyst. A few uncatalyzed reactions, however, have been documented, such as the following remarkably stereospecific transformations of (Z)-and ( )-hept-3-ene ... 

Heck reaction with acrylic acid can be carried out at room temperature if diaryliodonium salts are taken as the arylating agents in water [95]. At room temperature, only one aryl group of the iodonium salt is transferred to the product ... 

Both diazonium salts and iodonium salts can be effectively used as arylating agents. The aryl group is transferred either heterolyt-ically or homolytically, depending on the choice of salt and reaction conditions. In acid solution diazonium salts decompose relatively cleanly to give products consistent with a polar mechanism. In basic solution the product is a complex mixture resulting from free radical intermediates (6). When either benzenediazonium chloride or fluoborate is decomposed in acidic methanol, the major product, formed in 93% yield, is anisole, and less than 1% biphenyl is isolated. In the same solvent with an acetate buffer, the product contains 85-90% benzene, 4.5% biphenyl, 0.6% azobenzene, some anisole, and 80-90 mole % formaldehyde per mole of diazonium salt decomposed (7). 

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