Iodosylbenzene tetrafluoroborates

An explosion [1] of iodosylbenzene tetrafluoroborate attributed by Chem. Abs. to another structure is more likely to be of this, in view of the original synthetic papers [2],... 

Iodosovinyl chloride, 0687 Iodosylbenzene, 2245 Iodosylbenzene tetrafluoroborate, 2288 4-Iodosyltoluene, 2749 4-Iodotoluene, 2746 f Iodotrimethylsilane, 1302 4-Iodylanisole, 2751 Iodylbenzene, 2246 2-Iodylbenzoic acid, 2677 4-Iodyltoluene, 2750 2-Iodylvinyl chloride, 0688 Nitrogen triiodide—ammonia, 4630 Nitrogen triiodide—silver amide, 4629 Nitrogen triodide, 4628 Orthoperiodic acid, 4537... 

Vinyliodonium tetrafluoroborates.l These salts are obtained with retention of configuration by reaction of vinylsilanes with iodosylbenzene activated with triethyloxonium tetrafluoroborate (equation I). 

The best procedure for the preparation of these compounds involves alkenylsilanes and iodosylbenzene activated by either triethyloxonium tetrafluoroborate or boron trifluoride etherate. The reaction proceeds stereospecifically with retention of configuration. 

Boron trifluoride etherate (2.5 equiv. with respect to the alkenylsilane) was added dropwise to a stirred suspension of the appropriate alkenylsilane and iodosylbenzene (2.5 equivalent with respect to the alkenylsilane), in dichloromethane, under nitrogen. A yellow colour developed, while the mixture was stirred for 15 min to 7 h, at 0°C or room temperature, according to the substrate. A saturated aqueous sodium tetrafluoroborate solution was added and the mixture was stirred vigorously for 0.5 h. The reaction mixture was poured into water and extracted with dichloromethane. The organic layer was concentrated to give an oil which was washed several times with hexane and/or ether by decantation. Further purification was accomplished by repeated dissolution of the salt in dichloromethane or ethyl acetate followed by slow precipitation with hexane or ether. 

Vinyliodonium salts.3 Reaction of vinylsilanes (2) with iodosylbenzene catalyzed by BF3 etherate results in vinyliodonium tetrafluoroborates (3) in generally... 

The treatment of (trimethylsilyl)acetylene with iodosylbenzene and boron trifluoride etherate does not give ethynyl(phenyl)iodonium tetrafluoroborate, but leads instead to (E)-1 -trimethylsilyl-2-ethoxyethynyl(phenyl)iodonium tetrafluoroborate (equation 26)79. 

Two methods for the direct conversion of terminal alkynes to alkynyl(phenyl)iodo-nium tetrafluoroborates have been reported, but their generality has not been documented in the literature. The ter -butylethynyl salt has been prepared by the generation of lithium tert-butylethynyl(trifluoro)borate and its coupling with iodosylbenzene by the standard method (equation 29)80. The treatment of 1-pentyne and phenylacetylene with diphenyl-ju-oxodiiodine(III) bistetrafluoroborate in dichloromethane likewise affords the corresponding alkynyliodonium tetrafluoroborates (equations 30)29. 

Finally, vinyl(tri-rc-butyl)stannanes have also been utilized with iodosylbenzene and Meerwein s reagent126 for the synthesis of the ( rr-butylcyclohexenyl)iodonium tetrafluoroborate shown in equation 162 and with iodosylbenzene/BF3-etherate to give the (ketovinyl)iodonium salt shown in equation 169128. 

Diaryliodonium salts are the most stable and well-investigated class of iodonium salts. The first example of these compounds, (4-iodophenyl)phenyliodonium bisulfate, was prepared by Hartmann and Meyer in 1894 from iodosylbenzene and sulfuric acid [368]. Diaryliodonium salts Ar2l+ X are air- and moisture-stable compounds, whose physical properties are strongly affected by the nature of the anionic part of the molecule. In particular, diaryliodonium salts with halide anions are generally sparingly soluble in many organic solvents, whereas triflate and tetrafluoroborate salts have a better solubility. The chemistry of aryl-and heteroaryliodonium salts has been extensively covered in several reviews [361,369,370]. 

Preparation First representatives of alkenyliodonium salts, dichlorovinyl(phenyl)iodonium species, were reported by Thiele and Haakh in the early 1900s [436]. The first general synthetic approach to alkenyl(phenyl)iodonium salts was developed by Ochiai in the mid-1980s [437,438], This method is based on the reaction of silylated alkenes 299 with iodosylbenzene in the presence of Lewis acids, leading to the stereoselective formation of various alkenyliodonium tetrafluoroborates 300 in good yield (Scheme 2.85). 

A similar boron-iodine(III) exchange of alkenylboronic acids 303 with iodosylbenzene or (diace-toxyiodo)benzene in the presence of boron trifluoride etherate is an efficient alternative method for a selective preparation of alkenyl(phenyl)iodonium tetrafluoroborates 304 in excellent yields (Scheme 2.87) [440,441],... 

A common method for preparing alkynyl(phenyl)iodonium tetrafluoroborates involves the reaction of iodosylbenzene in the presence of triethyloxonium tetrafluoroborate or boron trifluoride etherate with alkynyl-silanes. For example, the complex of iodosylbenzene with triethyloxonium tetrafluoroborate (362) reacts with alkynylsilanes in dichloromethane at room temperature to afford alkynyl(phenyl)iodonium tetrafluoroborates 363 in good yield [496]. A variation of this procedure employs the complex of iodosylbenzene with boron trifluoride etherate (364) followed by treatment with aqueous NaBp4 [493,497] or sodium arylsulfonates to furnish, respectively, the appropriate alkynyl(phenyl)iodonium tetrafluoroborates 363 [483,487] or organosul-fonates 365 [488,489] (Scheme2.102) [498,499],... 

A modified method for the synthesis of alkynyl(phenyl)iodonium tetrafluoroborates 363 consists of the direct reaction of terminal alkynes with iodosylbenzene, a 42% aqueous solution of tetrafluoroboric acid and a catalytic amount of mercury oxide (Scheme 2.103) [500]. 

The unstable (3-oxoalkyl(phenyl)iodonium salts 762, generated in situ by a low-temperature reaction of silyl enol ethers 761 with a complex of iodosylbenzene and tetrafluoroboric acid (Section 2.1.9.5), have been utilized in synthetically useful carbon-carbon bond forming reactions with various silyl enol ethers (Scheme 3.298) and other C-nucleophiles to afford the respective products of C—C bond formation [209, 1014,1015]. 

Vinyl iodonium salts, prepared by reaction of vinylsilanes with iodosylbenzene and triethyloxonium tetrafluoroborate, have been found to be excellent educts for nucleophilic substitution by a variety of nucleophiles. Reaction with KCu(CN)p in DMF was thus possible and acrylonitrile derivatives prepared accordingly. 

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