Alkynyliodonium tosylates reactions

Likewise, alkynyliodonium tosylates can be coupled with dialkyl- and diphenyl cuprates 136 to afford the respective alkyl- and phenyl-substituted alkynes 137 (Scheme 56) [114]. An interesting example of this reaction involves the coupling of (trimethylsilyl)ethynyl iodonium triflate with cubyl cuprate generated in situ from iodocubane 138 [116]. 

Various 2-substituted benzofurans 165 are obtained by the interaction of iodo-nium salts 164 with sodium phenoxide in methanol (Scheme 63) [126, 127]. This reaction proceeds via the intramolecular alkylidene carbene insertion into the ortho-CH bond of the phenoxy ring. Furopyridine derivatives 167 can be prepared similarly by the intramolecular aromatic C-H insertion of the alkylidenecarbenes generated by the reaction of alkynyliodonium tosylates 166 with potassium salts of 4- or 3-hydroxypyridines [128]. 

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. 

Dialkyl 1-alkynylphosphonates (22) were formed in good to high yields by treatment of 1-alkynyliodonium tosylates (23) with trialkyl phosphites the reaction is exothermic with trimethyl phosphite but requires heating with triethyl or triisopropyl phosphite. The addition of trimethyl or triethyl phosphite to 3-alkylene-2-oxindoles (24) has led to new product types for a, -unsaturated carbonyl compounds, i.e. a stable tri-alkoxyphosphonium zwitterion (25), and a C-alkylated phosphonate (26). ... 

Reaction of vinylcopper reagents, 62, with alkynyliodonium tosylates results in conjugated enyne 63, [53] [Eq. (24)]. The reaction is stereospecific with retention of olefin geometry. By appropriate order of addition, either of the two possible isomeric trisubstituted olefin isomers, 63, can be obtained in good isolated yields and excellent (>99%) stereoselectivity. Likewise, conjugated diynes, 65, are obtained [54] in the reaction of dialkynylcuprates, 64, with alkynyliodonium tosylates [Eq. (25)]. This method may be used for the preparation of unsym-metrical diynes. The mechanism of these coupling reactions is not understood at present. 

Reaction of alkynyliodonium sulfonates, 9, in dry acetonitrile in the presence of catalytic amounts of AgOTs or CuOTf leads to the formation of alkynyl sulfonates, 70, in reasonable yields [Eq. (30)] [18], In a similar manner bis(alkynyliodonium) tosylates, 36, give modest yields of bisalkynyl tosylates, 71, accompanied by some monotosylates, 72 [Eq. (31)] [41]. 

Trialkyl phosphites undergo reaction with alkynyliodonium tosylates, resulting in dialkyl alkynylphosphonates, 102, via an Arbuzov-type process [78] [Eq. (55)]. 

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]. 

The alkynylation of phosphorus nucleophiles has been less investigated (Scheme 7). Ochiai and co-workers first demonstrated in 1987 that the alkynylation of triphenyl-phosphine was possible with alkynyliodonium tetrafluoroborate salts under light irradiation (Scheme 7, A) [69]. The reaction most probably involves radical intermediates. In 1992, Stang and Critell showed that light irradiation was not needed if alkynyliodonium triflates were used [70]. Later, this methodology could be extended to other triaryl- or alkyl phosphines [71, 72]. In 1990, Koser and Lodaya also reported the synthesis of alkynylphosphonates by the Arbusov reaction of alkynyliodonium tosylates with trialkyl phosphites (Scheme 7, B) [73]. Alternatively, the same compotmds can be obtained by the reaction of alkynyliodonium tosylates with sodium phosphonate salts [74]. 

The alkynylation of sulfur nucleophiles works well with alkynyliodonium tosylates and triflates as long as the sulfur atom is not too electron-rich, else oxidation reactions dominate. For example, alkynyl thiocyanates [38, 39, 75], thiotosylates [76], and phosphorodithioates [77] can be accessed in good yields (Scheme 8, A). The alkynylation of thioamides is also possible, but in this case the product obtained is imstable and spontaneously cyclizes to give a thiazole (Scheme 8, B) [78, 79]. The alkynylation of sulfinates with alkynyliodOTiium triflates or tosylates gives an efficient access towards alkynyl sulfones (Scheme 8, C) [80, 81]. If C-H bonds are easily accessible, carbene C-H insertion products can... 

The cyclopentene annulations can also occur in the reactions of alkynyliodo-nium salts with nitrogen- and sulfur nucleophiles (Scheme 61). Specifically, azi-docyclopentene 155 is formed upon treatment of octynyliodonium tosylate 154 with sodium azide in dichloromethane [123]. The reaction of alkynyliodonium salt 156 with sodium toluenesulfinate results in the formation of substituted indene 157 via alkylidene carbene aromatic C-H bond insertion [124]. 

Reactions of alkynyliodonium salts with multidentate nucleophiles can be employed for the synthesis of heterocyclic compounds. Recent examples include preparations of thiazoles, selenazoles, and 2-mercaptothiazoles by the treatment of alkynyliodonium mesylates or tosylates with thioamides, selenoamides, and ammonium dithiocarbamate (Scheme 62) [169-171]. A novel hetero-Claisen rearrangement of tricovalent iodine(III) intermediates was proposed to account for the 2,4-disubstitution pattern of the thiazoles [169]. 

The presence of catalytic amounts of cuprous triflate or silver(I) sulfonates exerts a remarkable influence on the activation energy and regiochemistry of alkynyl(phenyl)-iodonium tosylate and mesylate decompositions5,6. Such reactions proceed in acetonitrile at room temperature and afford moderate yields of alkynyl tosylates and mesylates (equations 82 and 83)5,6. It is noteworthy, however, that the treatment of alkynyliodonium triflates (R = n-Bu, r-Bu) with cuprous triflate in acetonitrile does not afford alkynyl triflates6. Silver(I) catalysis has similarly been applied to the conversion of bis(alkynyliodo-nium) tosylates to bisalkynyl tosylates (equation 84)43. As might be expected, mono-tosylate esters are also produced in these reactions. 

The strongly polarized C = C bond of alkynyliodonium salts, along with their propensity for Michael additions, predicts that they should be good 1,3-dipolarophiles. Indeed, reaction of arylethynyliodonium tosylates with arenenitrile oxides, 127, gives a mbtture of cycloadducts, 128 and 129, in 62-80% yields [91] [Eq. (59)]. Similarly, Me3SiC=CIPh OTf and various diazocarbonyl compounds, 130, result [92] in cycloadducts 131 [Eq. (60)]. Likewise, alkynyliodonium salts react with methyl and phenyl azide to give low yields of triazines, 132, as adducts [Eq. (61)]. 

Several heteroaryl(phenyl)iodonium organosulfonates have been prepared by the [3-1-2] cycloaddition reactions of alkynyliodonium salts with 1,3-dipolar reagents. The reaction of (arylethynyl)iodonium tosylates... 

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... 

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