Alkynyl iodonium salts

Another useful reagent for the preparation of alkynyl lodonium Inflates is [cyano(trifluoromethylsulfonyloxy)(phenyl)]iodine [/i7, 138, 139, 140] prepared from iodosobenzene, trimethylsilyl tnflate, and trimethylsilyl cyanide (equation 71). This reagent reacts with various stannylacetylenes under very mild conditions to form the corresponding alkynyl iodonium salts in high yields [139] (equation 72)... 

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). 

Other pseudo-halides are used for carbonylation. Phenyl fluorosulfonate (484) can be carbonylated to give benzoate[337]. Aryl(aryl)iodonium salts[338], aryl(alkenyl)iodonium salts (485)[339], and aryl(alkynyl)iodonium salts (486)[340] are reactive compounds and undergo carbonylation under mild conditions (room temperature, 1 atm) to give aryl, alkenyl, and alkynyl esters. Iodoxybenzene (487) is carbonylated under mild conditions in... 

Alkynyl(aryl)iodonium salts where aryl was the o-carboxyphenyl group were obtained from silylalkynes and o-iodosobenzoic acid [139]. It is noted that the first alkynyl iodonium salts were obtained in low yield from terminal alkynes. This approach was perfected recently, so that a range of substrates upon reaction with p-MeC6H4IO in aqueous HBF4, with catalysis by HgO, afforded alkynyl (tolyl)iodonium salts [140]. 

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 electrophilic phenyl(alkynyl)iodonium salts (77) have proven to be a ready participant in a wide range of complex transformations. That is, simple 1,2-shift of R or Nu can form new alkyne (79). As a more interesting feature for organic synthesis, Ochiai and co-workers have reported on a series of studies on... 

Apart from the above two major general reaction pathways, there are some further possibilities for instance, [bis(trifluoroacetoxy)iodo]benzene reacts as an ambident electrophile and is attacked by hard nucleophiles at its carbonyl carbon, whereas iodylarenes may react similarly from carbon rather than iodine. Alkynyl iodonium salts are actually tetraphilic electrophiles, whereas iodosylbenzene reacts also as a nucleophile from oxygen. Diaryl iodonium salts serve as arylating reagents, mostly homolytically other iodonium salts transfer groups such as perfluoroalkyl, vinyl, alkynyl or cyano to several nucleophiles in various ways. 

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. 

The same salt from acetylene afforded similarly adducts with furan and 1,3-diphenyl i sobenzofuran. A number of alkynyl iodonium salts underwent also [2 + 3] cycloaddition with dipolarophiles such as a-diazocarbonyl compounds, nitrile oxides, etc., allowing the preparation of iodonium salts with an alkenyl or a heterocyclic moiety [7],... 

A series of 2-jS-phenylsulphonylalkenyl iodonium salts (prepared from alkynyl iodonium salts and phenylsulphinic acid) upon base treatment underwent predominantly cyclization, in contrast to the sulphenyl and sulphinyl bearing analogues, which gave alkynes. 

Enynes were prepared in good yield from alkynyl iodonium salts and alkenylcopper reagents, stereospecifically. This approach was suitable for the synthesis of conjugated enynes, using a trisubstituted alkene with complete retention of its geometry [47], 1,3-Diynes were similarly obtained by coupling alkynyl iodonium... 

Appropriately substitued alkynyl iodonium salts afforded with nucleophiles cyclopentene derivatives. This annulation can be either [5 + 0], when all carbon atoms come from the alkyl chain of the alkynyl moiety, or a [2 + 3] process, in which three carbon atoms come from the nucleophile. Competition between [5 + 0] and [2 + 3] annulation may occur in some cases. 

Annulated products from alkynyl iodonium salts and nucleophiles... 

An alternative approach for alkynyl carboxylates involved reaction between [bis(acyloxy)iodo]benzenes and lithium acetylides [59]. Alkynyl iodonium salts afforded with sodium carboxylates in the presence of water 1-acyloxyketones heating in an excess of acetic acid gave similarly a-acetoxy ketones [60], Alkynyl tosylates and mesylates were obtained from the thermal decomposition of isolable alkynyl iodonium sulphonates. 

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. 

Thiocyanation was very effective with several alkynyl iodonium salts, in a simple process avoiding the previously used cyanogen chloride or mercury compounds best yields of alkynyl thiocyanates were obtained using potassium thiocyanate in DMF [66],... 

Another superior method using alkynyl iodonium salts involved the preparation of S-alkynyl O, O-dialkylphosphorodithioates high yields were obtained under phase transfer catalysis [67]. Similarly, with potassium p-toluenethiosulphonate were obtained esters of the general formula p-TolS02SC=CR [68]. 

Other pathways, with trimethylsilyl azide and the appropriate iodonium salts, involved the formation of 3-alkyl-1-azido-cyclopentenes (Table 9.3.) or Z-fi-azidoalkenyl iodonium salts [69], Several types of alkynyl iodonium salts afforded with lithium diphenylamide push-pull ynamines overcoming some inherent limitations of other methods. 

Of special importance was the synthesis of bicyclic tosylenamides in tandem reactions of appropriate tosylamide-containing alkynyl iodonium salts [71] ... 

Triphenylphosphine with alkynyl iodonium salts in sunlight gave quantitatively the corresponding phosphonium salts, some of which could not be obtained by other methods [73]. Trialkyl phosphites were also reactive towards alkynyl iodonium salts several diaikyl alkynylphosphonates were prepared in good yield, e.g. [74] ... 

A general synthesis of 1-alkynyl triphenylarsonium salts has been elaborated from alkynyl iodonium salts and triphenylarsine under mild conditions [75] ... 

In a related area, interest in the isolation of alkynyl iodonium salts has led to the synthesis of analogous isoelectronic xenon(II) derivatives. These have been obtained by reaction of XeF2 with BulC=CLi or RC=CSiMe3 in BF3 OEt2 (181) ... 

Acetylenic ethers and esters represent an important class of functionalized acetylene derivatives of the hypothetical alkynols, RC=COH. The chemistry of acetylenic ethers has been well developed since their first preparation about 100 years ago Several exhaustive reviews covering the literature on acetylenic ethers and their analogs up to 1985 have been published in the last 30 years. In contrast to acetylenic ethers, esters of alkynols were unknown until the mid-1980s when the first preparation of alkynyl tosylates was reported. In the following years a wide variety of alkynyl carboxylate, phosphate and sulfonate esters has been prepared from alkynyl iodonium salts. The chemistry of these novel derivatives of alkynols has been summarized in a recent review. In the last 10 years considerable interest and research activity has arisen toward alkynols themselves and such derivatives as alkynolate salts and silyl ynol ethers. The present chapter will cover the chemistry of acetylenic ethers and esters as well as related derivatives of ynols with emphasis on new developments in this subject during the last 5-10 years. 

The triple bond of alkynes constitutes one of the oldest, simplest and most valuable functional groups in organic chemistry. Besides the common hydrocarbon acetylenes, a wide variety of functionalized alkynes (1) are known that play an important role in numerous organic transformations. The latest members of the family of functionalized alkynes are the alkynyl iodonium salts (2). These compounds are a subgroup of the di-coordinated positively-charged 8-1-2 iodine species L2U (3)k The first example of this type of molecules (4) was initially reported exactly one hundred years ago in 1894 by the German chemists Hartman and Meyer. To date, the best known and most widely used members of this class of polycoordinated iodine compounds are the diaryliodonium salts... 

The reaction of sulfinates with alkynyl iodonium salts was successful, as these substrates are less easy to oxidize. Nevertheless, Waser and Chen demonstrated that EBX reagents can also be useful to synthesize alkynyl sulfones, as they allow a new one-pot procedure starting directly from Grignard reagents (Scheme 36) [161]. In this protocol, DABSO (DABCO-S02) is added after formation of the Grignard reagent. Addition of DME and TIPS-EBX 52 gives aryl alkynyl sulfones in 46-85% yield. Eor base sensitive substrates, it was also possible to start from aryl iodides and use a palladium catalyst. 

Weissmann, M., S. Baranton, and C. Coutanceau. Modification of carbon substrates by aryl and alkynyl iodonium salt reduction. Langmuir 26, 2010 15002—15009. 

Kang, S.K. Lee, H.W. Jang, S.B. Ho, P.S. (1996) Palladium-catalyzed cross-coupling reactions of aryl-iodonium, alkenyl-iodonium and alkynyl-iodonium salts and iodanes with terminal alkynes in aqueous-medium, Chem. Commun., 835-6. 

As mentioned in the previous section, the treatment of secondary phosphine oxides with alkynyl iodonium salts is a reliable method for the preparation of phosphorus-carbon(sp) bonds. This chemistry can be extended to secondary phosphites for the preparation of alkynylphosphonates (Schane 4.367) [541]. The reactions were carried out under mild conditions in reaction vessels that were open to the atmosphere. 

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