Triflates alkynyl iodonium

Alkynyl iodonium triflates prepared by the above reactions (equations 70,72, and 73) have become valuable reagents m organic chemistry, serving as premier... 

Using this method, several mesogen diacetylenes were obtained [49]. Palladium-catalysed coupling of an allylic cyclic carbonate with 1-pentynyl phenyliodonium tetrafluoroborate to give an enyne was highly successful [50]. Alkynyl iodonium triflates and lithium salts of diethyl 2-[(diphenylmethylene)amino]malonate were used for the preparation of alkynyl-a-amino acid derivatives, e.g. [51] ... 

Equally good yields were also obtained from alkynyl iodonium triflates without phase transfer catalysis [65]. With arenesulphinic acids in methanol the reaction stopped at the stage of Z-/J-sulphonylalkenyl iodonium salt [41]. 

Aryliodonium salts. Unsymmetrical diaryliodonium triflates and aryl(alkynyl)-iodonium triflates are readily synthesized from the title compounds by reaction with ArLi and alkynyllithium reagents, respectively. Ethylene is one of the byproducts. 

Single-crystal X-ray structural data have been reported for the following alkynyliodonium compounds the parent ethynyl(phenyl)iodonium triflate (368) [495], phenylethynyl(phenyl)iodonium tosylate (369) [477], cyanoethynyl(phenyl)iodonium triflate (370) [458], propynyl(phenyl)iodonium periodate (371) [502], trimethylsilylethynyl(phenyl)iodonium triflate (372) [503], 3,3,3-trifluoropropynyl(phenyl)iodonium triflate (373) [504], bis(alkynyl)iodonium triflate 374 [505] and complexes of ethynyl(phenyl)iodonium [506] and l-decynyl(phenyl)iodonium [507] tetrafluoroborates with 18-crown-6 (Figure 2.13). 

Fluoroalkyl(alkynyl)iodonium triflates 388 can be prepared by the reaction of triflates 387 and (trimethylsi-lyl)acetylenes (Scheme 2.112) [176],... 

A study of the regioselectivity of the 1,3-dipolar cycloaddition of aliphatic nitrile oxides with cinnamic acid esters has been published. AMI MO studies on the gas-phase 1,3-dipolar cycloaddition of 1,2,4-triazepine and formonitrile oxide show that the mechanism leading to the most stable adduct is concerted. An ab initio study of the regiochemistry of 1,3-dipolar cycloadditions of diazomethane and formonitrile oxide with ethene, propene, and methyl vinyl ether has been presented. The 1,3-dipolar cycloaddition of mesitonitrile oxide with 4,7-phenanthroline yields both mono-and bis-adducts. Alkynyl(phenyl)iodonium triflates undergo 2 - - 3-cycloaddition with ethyl diazoacetate, Ai-f-butyl-a-phenyl nitrone and f-butyl nitrile oxide to produce substituted pyrroles, dihydroisoxazoles, and isoxazoles respectively." 2/3-Vinyl-franwoctahydro-l,3-benzoxazine (43) undergoes 1,3-dipolar cycloaddition with nitrile oxides with high diastereoselectivity (90% de) (Scheme IS)." " ... 

The reaction of lithium or sodium arylteUurolate with alkynyl phenyl iodonium triflates or tosylates. ... 

The unique reactivity pattern of alkynyl iodonium salts discussed in Sections II,A.2 and II,D,la can also serve as two-carbon conjunctive reagents in the synthesis of pyrroles, dihydropyrroles, and indoles. Feldman et al. found that combination of alkyl or aralkyl tosylamide anions 101 with phenyl(propynyl)iodonium triflate (102) furnishes the corresponding dihydropyrroles 103 (95JOC7722) (Scheme 28). 

The AuCl-catalysed 4 + 2-cycloaddition of benzyne with o-alkynyl(oxo)benzenes produced anthracene derivatives having a ketone in the 9-position, in good to high yields under mild conditions.118 Hypervalent iodine compounds, [5-acyl-2-(trimethyl-silyl)]iodonium triflates, readily yielded acylbenzynes which could be trapped with furan.119 Both DMAD and benzyne reacted with borabenzene to yield substituted borabarrelenes and borabenzobarrelenes, respectively.120... 

A number of 1-hydroxybenziodoxoles and related heterocycles, more efficiently through their triflates, upon reaction with RC = CSiMe3 afforded either alkynyl iodonium salts or the corresponding cyclic iodanes, depending on the conditions. Some of these compounds reacted with NaN3 and were converted into /J-azidoalkenyl derivatives as illustrated in Scheme 55 [127,167,168]. 

The palladium/copper-cocatalyzed coupling of the readily available trisubsti-tuted alkenyl(phenyl)iodonium triflates 77 with alkynyl- and alkenylstannanes proceeds under exceedingly mild conditions with retention of geometry of the alkenyl ligand of the iodonium salt (Scheme 35) [60]. 

Under similar conditions, (2-oxoazetidinyl)malonates 129 can be alkynylated by (trimethylsilyl)ethynyl iodonium triflate (Scheme 53). In contrast to the previous reaction (Scheme 52), this alkynylation directly affords the desilylated terminal alkynes 130 as the final isolated products [112]. This reaction (Scheme 53) allows ethynylation of malonates under milder conditions compared to the reaction shown in Scheme 51. 

Instead of silyl-, stannylalkenes are also suitable precursors [4] cyano phenyliodonium triflate (Section 9.1.4) was here the reagent of choice. This variation enabled the preparation of the parent ethenyl and several trisubstituted alkenyl phenyliodonium triflates [5], More elaborate members were obtained through additions to the triple bond of alkynyl iodonium salts, notably Diels-Alder adducts. 

An interesting reaction between the bis phenyl iodonium triflate of acetylene and the silyl enol ether of acetophenone afforded an allene (PhCOCH=C=C=CHCOPh, 84%) [6], Also, alkynyl iodonium tosylates and carbon monoxide in methanol or ethanol, with palladium catalysis, furnished alkyne carboxylates [53]. 

The iodonium triflate (460 mg, 1 mmol) was added to a stirred slurry of anhydrous sodium p-toluene sulphinate (180 mg, 1.01 mmol) in dichloromethane (15 ml) at 20°C under nitrogen. After 15 min water (10 ml) was added and the phases were separated the aqueous layer was extracted with additional dichloromethane (2 x 5 ml), and the combined organic extracts were dried. The filtered solution was treated with hexanes (30 ml) and concentrated. The solid residue was purified by radial chromatography (silica gel, 200-400 mesh, dichloromethane-hexanes) to afford 3-tosyl-bicyclo[3.2.0]-3-heptene-2-one (197 mg, 75%), m.p. 164-165°C. The method is general for the preparation of sulphones with a cyclopentenone moiety other alkenyl iodonium salts gave alkynyl sulphones with sulphinates (Section 9.4.4). 

Sodium phenyloxide and alkynyl (p-phenylene)bis iodonium triflates afforded 2-substituted benzo[b]furans (Table 9.3). 

Sodium thiophenoxide and bis phenyliodonium acetylene triflate afforded cleanly l,2-bis(phenylthio)acetylene [6]. Alkynyl iodonium salts have alkynylated several arene sulphonates which were converted into alkynyl aryl sulphones. The process is probably the best among other methods, as far as yield, availability of starting materials, non-toxicity and ease of handling are concerned. 

The reactions of / -ketoethynyl- and ) -amidoethynyl(phenyl)iodonium triflates, 17 and 18, with sodium / -toluenesulfinate illustrate the synthetic potential of alkynyliodonium salts33. Although the direct attachment of a carbonyl group to the / -carbon atom of the triple bond in alkynyliodonium ions might be expected to facilitate alkynyl sulfone formation via the Ad-E mechanism, this mode of reactivity has not been observed. Instead, the MC pathway with carbenic insertion dominates and affords sulfones containing the... 

Photochemical activation is not universally required for the conversion of alkynyliodo-nium salts into alkynylphosphonium compounds. For example, triphenylphosphine reacts with various alkynyl(phenyl)iodonium triflates in dichloromethane to give high yields of alkynylphosphonium triflates (equation 71)90. Since these reactions occur readily in the dark and are not inhibited by molecular oxygen or 2,6-di-terr-butyl-4-methylphenol, they are thought to proceed via the MC mechanism (equation 45)90. 

The conversion of alkynyl(phenyl)iodonium ions to alkynyl esters with carboxylate ions via the MC mechanism (equation 45) has been proposed81. Evidence for the viability of this process is provided by the generation of 3,3-dimethyl-1-cyclopentenyl benzoate in addition to the expected alkynyl benzoate when the iodonium triflate shown in equation 90 is mixed with sodium benzoate in dichloromethane (yields not reported)3. 

Phenyl[(trimethylsilyl)ethynyl]iodonium triflate has also been employed for alkynylations of diethyl 2-phthalimidomalonate and the (2-oxoazetidinyl)malonates shown in equation 126. However, unlike the result with the [(diphenyl)amino]malonate system (equation 125), the trimethylsilyl group is lost, and the ethynyl group is ultimately introduced. 

Vaska s complex, the square planar iridium(I) compound shown in equation 145, readily interacts with alkynyl(phenyl)iodonium triflates in toluene at room temperature21. Such reactions proceed with loss of iodobenzene and deliver octahedral Ir(III) complexes possessing (7-alkynyl and trifluoromethanesulfonato ligands in a Jnms-relationship. The rhodium(I) analog of Vaska s complex behaves in a similar way21. 

Since it is known that halo(phenyl)acetylenes add oxidatively to Vaska s complex to give (7-phenylethynyl iridium(III) halides, 32112, the intervention of phenyliodonium iridium(III) and rhodium(III) intermediates, 33, in the alkynyliodonium reactions seems plausible. In any case, the production of cr-alkynyl complexes with alkynyl(phenyl)-iodonium triflates appears to be both more general and efficient21. 

Diels-Alder reactions of alkynyl(phenyl)iodonium triflates (i.e. containing electron-withdrawing groups in the alkynyl moiety) and [bis(phenyliodonium)] ethyne ditrifiate have been employed for the synthesis of cyclic vinyliodonium salts (equations 143 and 144)17,41. The availability of such compounds offers considerable potential for the elaboration of densely functionalized cyclic molecules. 

An intramolecular alkylidenecarbene addition is featured in a recent total synthesis of the tropoloisoquinoline alkaloid, pareitropone (02JA11600, 02JOC8528). More specifically, the pareitropone skeleton was assembled by base-catalyzed bicyclization of the alkynyl(biaryl)-iodonium triflate 266 to the tetracyclic compound 267, one step away from the target structure 268. The conversion of 266 to 267 is thought to occur via the carbene addition—norcaradiene isomerization sequence depicted in Scheme 75. Similar bicyclization of the methoxy analog of 266 (i.e., OMe vs. OTIPS) was also demonstrated. 

Alkynyl(phenyl)iodonium triflates react with pivaldehyde oxime in the presence of iodosylbenzene to give the isoxazoles 278 (Scheme 79) (97TL8793). Although the purpose of iodosylbenzene was to oxidize the oxime to the corresponding nitrile oxide, thus providing access to isoxazolyliodonium salts, its overall influence on the outcome of these reactions has not been firmly established. 

A Simple and Convenient Method for the Preparation of p-Functionalized Alkynyl(phenyl)iodonium Triflates Phenyl[p-toluenesulfonyl)ethynyl]iodonium Triflate. 

Coupling of alkenyl- or alkynyl-stannanes with alkenyl(phenyl)iodonium triflates leads to stereodefined dienes or enynes. ... 

A more general, simpler procedure [20] takes advantage of the in situ formation of the p-oxo-bis-triflate (6 R=CF3) and its interaction with a sila- or tin-acetylene [Eq. (2)]. This methodology affords a wide variety of stable, alkynyl(phenyl)iodonium triflates 10 in good to excellent yields and is applicable to the synthesis of the parent [21] ethynyl(phenyl)iodonium triflate (10 R=H) from n-Bu3SnC=CH. 

The best and most versatile contemporary method [22] of preparation of alkynyl(aryl)io-donium salts employs readily available alkynylstannanes [23], and the easily prepared [24] cyano(phenyl)iodonium triflate 7 as an iodonium transfer agent in dichloromethane at low temperatures [Eq. (3)]. This procedure provides excellent yields of iodonium triflates 10 and is applicable to a very broad range of alkynylstannanes, including those with strongly electron-withdrawing groups as summarized in Scheme 3-1. Particularly noteworthy and valuable are the P-keto- and P-amido-substituted species 11 and the cyano-functionalized molecule 11 (Y=CN) [25, 26]. 

Alkynyl(phenyl)iodonium carboxylates 99 are even less stable than phosphates 98 and decompose immediately upon generation from iodonium triflates 100 or benzoate 101 with the formation of the desired alkynyl carboxylates 96 (equation 65) k... 

The upheld shift of the a-carbon resonance is due to the spin-orbital effects of the heavy iodine atom. For alkynyl(phenyl)iodonium triflates there is an additional signal, centred at 121ppm (q, Jc—F 320 Hz), due to the carbon of the CF3SO3 moiety. 

Trimethylsilylalkynes can be converted to alkynyl(phenyl) iodonium triflates by treatment with PhI(OAc)2 and Tf20 (eq 88). Alkynyl(phenyl)iodonium triflates are useful electrophilic acetylene equivalents and can act as Michael acceptors, 1,3-dipolariphiles and alkynyl cation equivalents. ... 

---