Cyano iodonium triflate

A similar iodonium exchange reaction involves aryl(cyano)iodonium triflates 278 and stannylated aromatic precursors providing many kinds of diaryl or aryl(heteroaryl) iodonium salts [145,147,401], Tykwinski, Hinkle and coworkers have reported an application of such iodonium transfer reaction for obtaining of a series of mono- and bithienyl(aryl)iodonium triflates 279 with increasingly electron-withdrawing substituents on the aryl moiety (Scheme 2.81) [401], Thienyl and bithienyl iodonium salts prepared by iodonium transfer reaction using PhI(CN)OTf are potentially useful as nonlinear optical materials [402],... 

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],... 

Aryl(cyano)iodonium triflates 348 and 278 are prepared by reactions of iodosylbenzene or [bis(trifluoroacetoxy)iodo]arenes with trimethylsilyl triflate and cyanotrimethylsilane (Scheme 2.106). 

Cyanides 278 are relatively stable, white microcrystalline solids that decompose over several days at room temperature, but can be stored for extended periods in a refrigerator without change [146, 508], Phenyl(cyano)iodonium triflate (348) has found some synthetic application as the iodo-nium transfer reagent useful for preparation of various iodonium salts (Sections 2.1.9.1.1, 2.1.9.2.1 and 2.1.9.3.1). 

In contrast to the previous method (equation 70), reaction 72 made possible the preparation of iodonium triflates from functionalized acetylenes bearing an electron-withdrawing group such as tosyl, cyano, or carbonyl [138]. Of special interest is the application of this method to the synthesis of the bisiodonium acetylenic salt [139, 140] (equation 73). 

Cyano)(trifluoromethanesulfonoxy)-iodojbenzene or cyano(phenyl)-iodonium triflate... 

Stang and co-workers361-363 have reported the synthesis of the triflate salts of dialkynyliodonium ions (142), the phenyl(cyano)iodonium ion 143 and the dicya-noiodonium ion 144. 

Instead of silyl-, stannylalkenes are also suitable precursors [4] cyano phenyliodonium triflate (Section 9.1.4) was here the reagent of choice. This variation enabled the preparation of the parent ethenyl and several trisubstituted alkenyl phenyliodonium triflates [5], More elaborate members were obtained through additions to the triple bond of alkynyl iodonium salts, notably Diels-Alder adducts. 

The overwhelming majoritiy of currently known alkynyliodonium species are prepared by interaction of a terminal, sila- or tin-acetylene with an electrophilic X -iodane, also referred to as a 10-1-3 hypervalent species [14]. Key reagents are iodosobenzene (4), [hydroxyftosyl-oxy)iodo]benzene (5, HTIB) [15] the -oxo-X -iodane 6 [16], and cyano(phenyl)iodonium triflate 7 [17]. 

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 for preparing alkynyl(phenyl)iodonium triflates employs the iodonium transfer reaction between cyano(phenyl)iodonium triflate (348) and alkynylstannanes. The interaction of a large variety of readily available p-functionalized alkynylstannanes 349 with reagent 348 under very mild conditions provides ready access to diverse p-functionalized alkynyliodonium salts 350 in excellent yields (Scheme 2.100) [458,482,483]. This procedure is particularly useful for the preparation of various complex. 

Two structural types of cyanoiodonium salts are known (dicyano)iodonium triflate, (NC)2lOTf [399,400] and aryl(cyano)iodonium derivatives, Arl(CN)X [ 146,460,508,509]. (Dicyano)iodonium uiflate 277 can be prepared by the reaction of iodosyl triflate (375) (Section 2.1.1.2) with cyanotrimethylsilane in dichloromethane (Scheme 2.105). In the solid state, compound 277 is thermally unstable and air-sensitive it completely decomposes at room temperature in 2-5 min forming cyanogen iodine, ICN and explodes when exposed to air. However, it can be stored at -20 °C under nitrogen for several days [400]. Despite its low stability, cyanide 277 can be used in situ for the very mild and efficient preparation of various bis(heteroaryl)iodonium salts by an iodonium transfer reaction with the respective stannylated heteroarenes (Section 2.1.9.1.1). 

The reactions of vinyl(tri-n-butyl)stannanes with the appropriate [cyano(sulfonyloxy)-iodo]benzenes in dichloromethane constitute a facile stereoselective approach to / ,/ -disubstituted vinyl(phenyl)iodonium tosylates and triflates (equation 168)130,131. Although this method has not yet been used for the preparation of a,/ -disubstituted and a,/ ,/ -trisub-stituted analogs, it has been applied to the synthesis of ethenyl(phenyl)iodonium triflate131. The efficiency of this approach may be contrasted with the early work on chlorostannanes and chloroiodanes. 

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