Bis iodonium

Alkylidenecarbenes 40 generated by the reaction of alkynyl p-phenylene)bis-iodonium ditriflates 39 with phenoxide anion undergo selective intramolecular aromatic C—H insertion, thereby providing 2-substituted benzofurans 41 (93TL4055) (Scheme 15). 

A similar procedure was used for the preparation of several bicyclic enediynes 78 from bis-iodonium salts 62 and alkynylstannanes (Scheme 36) [61]. This coupling reaction was recently utilized in the synthesis of novel dinu-clear complexes with a photochromic bridge [62]. 

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]. 

Other alkynyl phenyliodonium arylsulphonates were prepared by modified procedures, notably from iodosylbenzene and alkynylsilanes, in good yields (62-89%). The decomposition stage proceeded also in satisfactory yields, up to 88% [61]. Bis alkynyl dibenzoates and ditosylates were prepared from the corresponding bis iodonium salts of the general formula PhI+C=C(CH2) C=CI + Ph, where n = 5,6,8 [62]. 

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

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

An alternative single source C4 precursor is the electrophilic bis(iodonium) triflate [PhIC=CC=CIPh](OTf)2, which reacts with Yaska s complex in acetonitrile to give unstable pale brown [ trans-IrCl(CO) (NCMe)(PPh3)2 2((i-C=CC=C)](OTf)2 (124).239 With ra s-RhCl(CO) (PPh3)2, only uncharacterized polymeric material was formed. 

Treatment of alkynylsilanes with 22, prepared from iodosobenzene and two molar equivalents of CF3SO3H, in acetonitrile results in the bis-iodonium (p-phenylene) bistriflates 23 in yields of 49-83% [Eq. (12)] [34]. 

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)]. 

Similarly, tethered conjugated as well as nonconjugated bis-iodonium diyne bistriflates 34, 35 [40], and ditosylates 36 [41], have been reported [Eqs. (17), (18)]. Reaction of the respective bis-tin-alkynes with two equivalents of 7 results in good to excellent yield of the corresponding bis-iodonium diynes 34-36. 

In general, the parent ethynyliodonium salts and simple alkyl-substituted compounds ate the most stable and may be indefinitely stored as pure solids in a refrigerator. The P-func-tionalized (11) and bis-iodonium (34-36) compounds are somewhat less stable but may be isolated, characterized, and stored cold for several days in pure form. The stability of both the diynyliodoniums 26 and the dialkynyl compounds 28 are greatly dependent upon the substituents R. The greater the steric bulk of R, the more stable the compound. Perhaps, the least stable, fully characterized species is the bis-iodonium diyne 32, which decomposes rapidly above — 20°C and hence is best made fresh and used in situ. 

The large majority of alkynyliodonium salts, and all alkyl-substituted ones are white or off-white in color. Some P-functionalized (11) and conjugated bis-iodonium (34, 38) compounds are yellow. 

With bis-iodonium salts 56, bis-insertion products 57-59 are observed [52], as summarized in Scheme 3-6. 

Scheme 3-6 Bis-cyclopentene formation via double Michael addition and carbene insertions in the reaction of nucleophiles with bis-iodonium diynes.

Likewise, the bis-iodonium diyne triflates 34 and 35 give the bisphosphonium diynes 96 and 97 in high isolated yields [40] [Eqs. (51), (52)]. 

Scheme 3-10 Diels-Alder cycloaddition of bis-iodonium ethyn 30, with cyclopentadiene and furans and subsequent reaction of the adducts.

General Procedure for the Preparation of Bis-iodonium Diyne Bis-triflates, 34 and 35... 

Likewise, this methodology is well suited for the preparation of novel bis(iodonium)ethyne (24) (equation 8) as well as bis(iodonium)diynes (25-27). This procedure is also applicable to the preparation of buta-l,3-diynyl(phenyl)iodonium trifiates (28) (equation 9). The use of iodosyl trifiate (29) and two equivalents of silylacetylene affords the dialkynyliodonium salts (30) (equation 10). ... 

Reaction of alkynyl(p-phenylene)bis-iodonium ditriflates 34 with sodium phenoxide in methanol provides 2-substituted benzofurans in 49-62% yields. The starting materials 34 were prepared readily by interaction of 33 with 1-trimethylsilylalkynes <97JCS(P2)1511>. 

The preparation and chemistry of cyclic iodonium salts has been summarized in a review of Grushin [361]. Several examples of known cyclic iodonium salts are shown in Figure 2.10 and include 4,5-phenanthryleneiodonium salts (239) [362], 10//-dibenz[fe,e]iodinonium salt (240) [363], 10,11-dihydrodibenz[fe,/]iodeponium salt (241) [363], phenoxiodonium salt (242) [363], 10-acetylphenaziodonium salt (243) [363], 10-oxidophenothiiodonium salt (244) [363], the bicyclic bis-iodonium salt 245 [364], ben-ziodolium chloride 246 [359] and iodolium salt 247 [365],... 

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... 

Structural Studies Examples of alkenyliodonium salts whose X-ray crystal structures have been reported in literature include the following ( )-((3-trifluoromethanesulfonyloxyalkenyl)phenyliodonium triflate 336 [465], 2,3-bis(iodonium)norbornadiene 332 [460], 4-fert-butylcyclohexenyl(phenyl)iodonium... 

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). 

Various iodonium salts are potent sequestering agents for PQQ [161]. In particular, bis-iodonium salts 54 and 55 inhibit PQQ at a nanomolar level (7-13 nM) and are nearly a 1000 times better inhibitors of PQQ than PhalCl and DPI (52). The potential implication of this activity is in the possible uses of bis-iodonium salts as biocides and in particular as a new class of antimicrobial agents [161]. 

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