Iodosyl triflates

A similar electrophile, iodosyl triflate, CF3S020I0, was employed with arylsi-lanes [98]. The same reagent upon reaction with Me3SiCN formed (CN)2I+ TfO" which was coupled with tributyltin substituted arenes or heterocycles to afford bis(heteroaryl)iodonium triflates, e.g. dithienyl and difuryl derivatives [99]. However, this method gave poor results with nitrogen heterocycles. For them another approach was developed based on the reaction of the appropriate lithium compound with / -(dichloroiodo)chloroethylene (Scheme 33). Pyridine and quinoline compounds were formed in this way in moderate yield (23-71 %) [100]. 

Trimethylsilyl cyanide (0.54 ml, 4 mmol) was added to a stirred suspension of iodosyl triflate (0.58 g, 2 mmol) in dichloromethane (15 ml) at — 78°C under nitrogen. The mixture was allowed to warm to — 20°C and stirred at this temperature for 15 min until the formation of a clear solution. The solution was cooled to — 78°C and transferred to a cold stirred solution of the appropriate tributyltin heterocycle (4 mmol) in dichloromethane (15 ml). The mixture was brought to room temperature and crystallized by the addition of dry hexane (20-30 ml). The precipitated iodonium salt was filtered under nitrogen, washed with dry ether (30 ml) and dried in vacuo. Mono or bis hetaryl iodonium salts prepared by these and related methods also involved groups coming from selenophene [23], pyrazoles [24], benzothiophene [21], etc. 

Reaction of butadiynyltributylstannanes 25 with 7 in dichloromethane at — 40 °C results in the corresponding l,3-diynyl(phenyl)iodonium triflates 26 [Eq. (13)] [36]. These novel iodonium salts represent a new type of functionalized, conjugated diyne as well as an interesting iodine(III) species. Iodonium salts bearing two alkynes as organic ligands are also known [37]. These species, 28, are prepared by the reaction of sila-alkynes with iodosyl triflate, 27 [Eq. (14)] [38]. 

A very mild and general method for the preparation of diaryl- and heteroaryliodonium triflates is based on iodonium transfer reactions of iodine(III) cyanides with the respective aryl- or heteroarylstannanes [146,148, 399-401]. Specifically, (dicyano)iodonium triflate (277), generated in situ from iodosyl triflate and MesSiCN, reacts with tributyltin derivatives of aromatic and heteroaromatic compounds to afford the corresponding symmetrical iodonium salts under very mild conditions (Scheme 2.80) [389,390]. 

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). 

Iodosyl fluorosulfate, OIOSO2F and the triflate, OIOTf, can be prepared as thermally stable, hygroscopic yellow solids by the reaction of iodine with iodine pentoxide or iodic acid in fluorosulfonic or trifluoromethanesulfonic acids, respectively [5]. Raman and infrared spectra of these compounds indicate a polymeric structure analogous to iodosyl sulfate [5], Iodine tris(fluorosulfate), I(0S02F)3 and tris(triflate), I(OTf)3, are also known [6,26]. I(0S02F)3 can be prepared by the reaction of iodine with peroxydisulfuryl ditluoride [26]. Salts such as KI(0S02F)4 have also been prepared and investigated by Raman spectroscopy [26,27]. I(OTf)3 was prepared from iodine tris(trifluoroacetate) and trifluoromethanesulfonic acid [6]. 

Ar2l+HS04, in several consecutive steps. Other inorganic iodosyl derivatives, such as iodosyl fluorosulfate (256) and iodosyl trifluoromethanesulfonate (258) also react with arenes or trimethylsilylarenes under mild conditions to afford the corresponding iodonium hydrosulfates 257 or triflates 259 (Scheme 2.73) [373,374],... 

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