Alkynes hydroxy iodo benzenes

Chiral iodonium salts of the general type p-RC6H4C = CI+Ph X-, where R was S-2-methylbutyloxy or S-2-methylbutyloxycarbonyl and X was TsO or TfO, were prepared from silylated alkynes with either [hydroxy(tosyloxy)iodo]benzene or PhI(OTf)OI(OTf)Ph [138]. 

Polymer-bound alkynyl(phenyl)iodonium salts were prepared by refluxing polymer-bound [hydroxy(tosyloxy)iodo]benzene and some alkynes in dry chloroform [141]. 

Alkynyl dialkyl phosphates of the general formula RC=COPO(OR )2, were prepared by a similar spontaneous decomposition of the less stable salts RC=CI+ PhC OPO(OR)2, some of which are isolable alternatively, either alkynes and [hydroxy(dialkylphosphoryloxy)iodo]benzene or alkynysilanes and iodosylben-zene-boron trifluoride can be used [63]. 

Hydroxy(tosyloxy)iodo]benzene and Its Analogues Reactionswith Alkenes and Allenes. Reactions with Alkynes and Alcohols. Reactions with Keto Compounds. Reactions with Nitrogen, Sulfur, and Other compounds. 

The synthesis of the first alkynyliodonium tosylates was achieved by the treatment of terminal alkynes with [hydroxy(tosyloxy)iodo]benzene (HTIB) (equation 8)8,10,11. Such reactions are generally conducted with an excess of alkyne in chloroform at reflux, although they can be carried out at room temperature, and dichloromethane can be employed as solvent. This procedure is, however, restricted to terminal alkynes in which R is either an aryl group or a bulky alkyl group. With linear alkyl groups (i.e. R = n-Pr, n-Bu, fl-C5Hn), phenyl(/ -tosyloxyvinyl)iodonium tosylates are obtained instead (equation 9)8. In some cases (R = /-Pr, /-Bu), mixtures of alkynyl- and (/ -tosyloxyvinyl)iodonium tosylates are produced8. ter -Butylacetylene appears to be the optimum substrate for this approach and has been employed with a series of [hydroxy(tosyloxy)iodo]arenes for the synthesis of various aryl(ter/-butylethynyl)iodonium tosylates (equation 10)9. 

While vinylsilanes and -stannanes have been used primarily for the synthesis of vinyliodonium salts with one or two / -alkyl substituents in the vinyl moiety, the treatment of alkynes with oxyiodanes permits the introduction of oxygen functionality at jft-carbon. The conversion of terminal alkynes with [hydroxy(tosyloxy) iodo]benzene (HTIB) to alkynyliodonium tosylates (equation 8) and/or (j5-tosyloxyvinyl)iodonium tosylates [TsOC (R)=CHiPh, "OTs R = n-Pr, n-Bu, n-C5Hn, i-Pr, i-Bu] (equation 9), depending on the size of R, has already been discussed8,11. In at least three cases, E Z mixtures were... 

The only known alternative procedure for the preparation of alkynyl(phenyl)iodonium arylsulfonates, the latest member of the family of polyvalent Iodine compounds, involves the reaction of [hydroxy(tosyloxy)iodo]benzene. PhlOH-OTs, with terminal alkynes as first reported by Koser and elaborated by us. This procedure has a number of shortcomings. Formation of the desired alkynyliodonium salt is usually accompanied by a related vinyl species, R(TsO)C=CHIPh-OTs, that both decreases the yields and causes purification problems. Furthermore, when the alkyl substituent of the starting alkyne is small, such as CH3, n-Pr, n-Bu, etc., this procedure gives either no product or low yields at best. 

In contrast, alkynyl dialkyl phosphate esters, 78, are formed in good isolated yields by either the treatment of alkynyliodonium triflates with (R0)2P02Na or the reaction of terminal alkynes with [hydroxy(phosphoryloxy)iodo]benzene, 77 [Eq. (34)], or the sequential treatment of alkynylsilanes with PhIO Et20Bp3 followed by aqueous (R0)2P02Na [Eq. (35)) [61]. These new, alkynyliodonium-derived, acetylenic esters have potent biological activity [4] in particular, the alkynyl benzoates are protease inhibitors [62], whereas the alkynyl dialkylphos-phates, 78, are inhibitors of a bacterial phosphotriesterase [63]. 

Oxidative cleavage of acetylenes RC=CH (R = Ph, Bu, hexyl, heptyl, cyclopentyl or PhCH2CH2) with bis[trifluoroacetoxy)iodo]pentafluorobenzene in wet benzene gives carboxylic acids RC02H. Alkynes 263 (R, R = H, Me, Et, Pr, Bu or Ph) undergo an oxidative rearrangement by the action of [hydroxy(tosyloxy)iodo] benzene in methanol to yield the esters 264. ... 

Initial methods of preparation of alkynyl(phenyl)iodonium compounds, as the tosylate salts (11), involved the interaction of terminal alkynes with [hydroxy-(tosyloxy)iodo]benzene (10) (equation 3). This method, however, suffers from lack of generality, low product yields, and separation problems from the concomitantly formed vinyl species (12) (equation 3). Recent modifications and improvements in this procedure have resulted in wider applicability and product yields of 60-90% of iodonium tosylates (11). 

Preparation A common synthetic approach to alkynyliodonium salts involves the reaction of an electrophilic X -iodane with a terminal alkyne or its silylated, stannylated, or lithiated derivative. In the early 1980s, Koser and coworkers found that [hydroxy(tosyloxy)iodo]benzene 75 reacts with terminal alkynes 344 upon gentle heating in chloroform or dichloromethane to form alkynyliodonium tosylates 345 in moderate to low yield (Scheme 2.98) [199,471,476]. 

This reaction (Scheme 2.98) works well only for alkynes 344 with a bulky alkyl or an aryl group as the substituent R. The addition of a desiccant to the reaction mixture results in broader applicability of this procedure with a greater variety of alkynes [477,478]. This method is also applicable to the preparation of alkynyliodonium mesylates and p-nitrobenzenesulfonates by the reaction of the appropriate [hydroxy(organosulfonyloxy)iodo]benzenes with terminal alkynes under similar conditions [477,478]. This procedure has been applied for the preparation of arylethynyl(phenyl)iodonium tosylates 347 bearing long... 

Hydroxy(dialkylphosphoryloxy)iodo]benzenes 177 (Section 2.1.7) react with terminal alkynes under anhydrous conditions to afford alkynyl phosphates 178 (Scheme 3.76) via intermediate formation of the respective alkynyl(phenyl)iodonium phosphates [239]. 

Analog of HTIB. Various derivatives of HTIB with substituents in the iodoarene nucleus, ArI(OH)OTs, and three arenesnlfonyloxy analogs have been reported. [Hydroxy (mesyloxy)Iodo] benzene, PhI(0H)03SMe, and [hydroxy((+)-10-camphorsulfonyloxy)iodo]benzene are also known. [Hydroxy ((bis (pheny loxy) phosphoryl) oxy) iodobenzene], PhI(0H)0P(0)(0Ph)2, shows considerable potential for phosphate ester synthesis. Thus far, the a-oxyphosphorylation of ketones and -dicarbonyl compounds, the oxyphosphoryllac-tonization of alkenoic acids, and the conversion of terminal alkynes to monoketol phosphates with HPIB have been reported. 

SCHEME 12 Isoxazoles via I(IIl)-mediated cydoaddition of aldoximes and alkynes. HT ltS, [hydroxy(tosyloxy)iodo]benzene. 

---