Bis-iodonium acetylene

The bis-iodonium acetylene 198 is even more reactive than 189 and undergoes Diels-Alder reaction with cyclopentadiene, furan and 1,3-diphenylisoben-zofuran in acetonitrile under very mild conditions (Scheme 71) [139]. All adducts (62,199) are isolated in the form of stable microcrystalline solids products 62 can be reacted further with nucleophiles or combined in a cross-coupling reaction with lithiated or stannylated alkynes [52,53,61]. 

A number of interesting bis-iodonium acetylenes and bis-iodonium diynes were reported in the early 1990s. Reaction of bis-tin-acetylene 29 and bis-tin-diyne 31 with two equivalents of 7 in cold dichloromethane results in the formation of novel bis-iodonium ethyne 30 [24] and bis-iodonium diyne 32 [39], respectively [Eqs. (15), (16)]. 

Several iodonium- and bis(iodonium) norbomadienes and other polycyclic adducts have been synthesized by [2-1-4] cycloaddition reactions of alkynyliodonium triflates with cyclic 1,3-dienes [458,460-464]. In particular, the bis-iodonium acetylene 331 undergoes Diels-Alder reactions with cyclopentadiene 329, furan... 

This procedure has been used for the preparation of the bis-iodonium acetylenes 356 and 357 [460,488], conjugated 358 and unconjugated 359 bis(alkynyliodonium) salts [489-491], tris(alkynyliodonium) salts 360 [491] and diynyl(phenyl)iodonium triflates 361 [492] (Scheme 2.101). 

Diphenyloxyacetylene was prepared from lithium phenyloxide and a bis iodonium salt of acetylene. 

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. 

Hydroxy(tosyloxy)iodobenzene 2014 reacts with phenyltrimethylsilane 81 in boiling acetonitrile to give diphenyliodonium tosylate 2015 and trimethylsilanol 4 or HMDSO 7 [184, 185]. Likewise, treatment of 2,5-bis(trimethylsilyl)furan 2016 with 2014 in boiling acetonitrile/methanol affords 78% iodonium tosylate 2017 and trimethylsilanol 4 [185]. In the presence of Bp3-OEt2 iodosobenzene oxidizes allyl-trimethylsilanes such as 2018 to unsaturated aldehydes such as 2019 in 63% yield, with formation of iodobenzene and trimethylsilanol 4 [186]. Analogously, vinyltrimethylsilanes such as (Z)-l-trimethylsilyl-2-phenylethylene 2020 afford, via 2021, acetylenes such as phenylacetylene in 61% yield and iodobenzene and trimethylsilanol 4 [187] (Scheme 12.54). 

The benzoiodoxol 2035 is converted by Me3SiN3 19 into 2036, which oxidizes cyclohexene to a-azidocyclohexanone 2037 [192], whereas 2035 reacts with bis(trimethyl-silyl)acetylene 2038 to give the iodonium salt 2039 [193] (Scheme 12.57). 

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]. 

Iodofluorination reactions of acetylenes can be carried out with iodine fluoride, prepared directly from the corresponding elements,553 with jV-iodosuccinimide in the presence of polymer-supported hydrogen fluoride,258 with (difluoroiodo)mcthane,554 or with bis(pyridine)iodonium tetrafluoroborate in the presence of fluoride.555 Some examples are summarized in Table 45. 

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. 

A very mild and selective approach to aryl- and hetaryliodonium chlorides 282 is based on the reaction of aryllithium 280 (generated in situ from bromoarenes and butyllithium) with ( )-chlorovinyliodine(in) dichloride (18) (Scheme 2.82) [71,88,89,403,404]. Tlie iodonium transfer reagent 18 is prepared by the reaction of iodine trichloride with acetylene in concentrated hydrochloric acid (Scheme 2.8 in Section 2.1.3.2) [403] caution this compound is highly unstable and should be handled and stored with proper safety precautions [71]. However, the iodonium transfer procedure with reagent 18 is particularly useful for the preparation of bis(hetaryl)iodonium chlorides 283 from the appropriate nitrogen heterocycles 282 (Scheme 2.82) [71]. 

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