Iodosylbenzene-Boron trifluoride etherate

Diphenylboryl trifluoromethane-sulfonate, 340 Ethyldimesitylborane, 8 Iodosylbenzene-Boron trifluoride etherate, 151... 

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. 

To a suspension of iodosylbenzene (1.1 g, 5 mmol) and the appropriate 1-trimethylsilyl-l-alkyne (5 mmol, prepared from 1-alkyne and trimethylchlorosilane in nearly quantitative yield, or obtained commercially) in chloroform (10 ml) was slowly added boron trifluoride etherate (710 mg, 5 mmol) at 0°C. The mixture was stirred at room temperature for 3-4 h, then recooled at 0°C and a solution of p-toluenesulphonic acid hydrate (3.8 g, 20 mmol) in water (20 ml) was added the resulting mixture was stirred vigorously for a few minutes. The organic phase was separated and the aqueous phase was washed with additional chloroform. The combined organic phase was washed with water, dried and concentrated. The residual oil solidified upon addition of ether. The solid was filtered, washed with ether and air-dried to give alkynyl phenyliodonium tosylates (62-89%). 

The first alkynyliodonium salt, (phenylethynyl)phenyliodonium chloride, synthesized in low yields from (dichloroiodo)benzene (3) and lithium phenylacetylide (equation 1), was reported in 196526. This chloride salt is unstable and readily decomposes to a 1 1 mixture of chloro(phenyl)acetylene and iodobenzene. It was not until the 1980s, however, that alkynyliodonium salts became generally available. This was made possible by the introduction of sulfonyloxy-/l3-iodanes as synthetic reagents46 and by the recognition that iodosylbenzene (4) can be activated either with boron trifluoride etherate or with triethy-loxonium tetrafluoroborate31. These reagents are now widely employed for the conversion of terminal alkynes and their 1-silyl and 1-stannyl derivatives to alkynyliodonium salts (equations 2 and 3). A more exhaustive survey of iodine(III) reagents that have been... 

When iodosylbenzene is treated with boron trifluoride etherate, it is both depolymer-ized and rendered more electrophilic, presumably because of the formation of a Lewis acid-base adduct (equation 4). 

The incorporation of propyne and 1-hexyne into alkynyliodonium salts with HTIB and its mesyloxy analog has been accomplished with the aid of a silica bead desiccant (equation ll)5,6, but the yields of the products are low. A better method for the synthesis of alkynyliodonium tosylates in which R is a linear alkyl group entails the treatment of (trimethylsilyl)alkyne/iodosylbenzene mixtures in chloroform with boron trifluoride etherate. When aqueous sodium tosylate is added to the resulting solutions, alkynyliodonium tosylates are produced and can be isolated from the organic phase (equation 12)7. The... 

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. 

The use of Moriarty s hypervalent iodine system (vide supra) has been extended to reaction with silyl enol ethers. In this case a more activated electrophile is required and the reactions are carried out with iodosylbenzene in the presence of boron trifluoride etherate. However, yields are only moderate and the process seems less useful than the corresponding ketone/enol application. 

The reaction of an allylmetal derivative of group IV (M = Si, Sn or Ge) with aromatic substrates in the presence of the complex iodosylbenzene-boron trifluoride-diethyl ether results in carbon-carbon bond formation realizing the allylation of the aromatic substrate in generally good yields.236,237... 

Another protocol uses a similar tin-iodine(III) and silicon-iodine(III) exchange reaction of (diace-toxyiodo)arenes or iodosylbenzene with tetraphenylstannane or (trimethylsilyl)benzene in the presence of boron trifluoride etherate [397]. 

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],... 

Iodosylbenzene-Dicyclohexylcarbodiimide-Boron trifluoride diethyl ether,... 

Closely related reactions are the self-coupling of P-dicarbonyl compounds upon treatment either with iodosylbenzene in the presence of boron trifluoride-diethyl ether in neutral solvents,234 or with iodobenzene diacetate in acetic acid. 235... 

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