Iodonium transfer reagent

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]. 

A very general and mild procedure for the stereospecific synthesis of aIkenyl(aryl)iodonium triflates 309 involves aryl(cyano)iodonium triflates 308 as iodonium transfer reagents in reactions with stannylated alkenes 307 (Scheme 2.89) [367,443,444], This method was also applied to the preparation of the parent vinyliodonium triflate from tributyl(vinyl)tin [445],... 

The most versatile method for preparing alkynyl(phenyl)iodonium triflates employs the iodonium transfer reaction between cyano(phenyl)iodonium triflate (348) and alkynylstannanes. The interaction of a large variety of readily available p-functionalized alkynylstannanes 349 with reagent 348 under very mild conditions provides ready access to diverse p-functionalized alkynyliodonium salts 350 in excellent yields (Scheme 2.100) [458,482,483]. This procedure is particularly useful for the preparation of various complex. 

Cyanides 278 are relatively stable, white microcrystalline solids that decompose over several days at room temperature, but can be stored for extended periods in a refrigerator without change [146, 508], Phenyl(cyano)iodonium triflate (348) has found some synthetic application as the iodo-nium transfer reagent useful for preparation of various iodonium salts (Sections 2.1.9.1.1, 2.1.9.2.1 and 2.1.9.3.1). 

In recent years, a variety of hypervalent iodine reagents have been available. The versatility of these hypervalent organoiodine reagents in organic synthesis has been well recognized. Diaryliodonium salts constitute an important reagent class for the transfer of aryl groups. These iodonium ion salts have been used effectively in C-arylation of a variety of nucleopohiles.112 The arylation of the anion of nitroalkanes with diaryliodonium salts was already reported in 1963.113... 

For both modern reagents PIFA and MoCls an inner-sphere radical transfer is expected, as depicted in Scheme 7. The Lewis acidic additives involved in the PIFA-mediated transformation create an iodonium species that forms a Jt-com-plex 26 with the substrate this subsequently leads to an electron transfer. In contrast, the electrophilic molybdenum chloride most probably coordinates to the oxygen atoms of the donor functions which will then start the transformation. Smooth conversions are obtained if the substituent R" adjacent to the donor (27) is another methoxy group or a bulky moiety. 

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. 

Iodonium salts are excellent reagents for C-arylation of a variety of keto compounds. These reactions proceed homolytically through radical-chain or radical non-chain processes, starting either by one-electron transfer to form radical pairs or by formation of iodanes as illustrated in a simplified way ... 

Other coupling partners to organozinc reagents include heterocyles such as 2-methylthiobenzothiazole, alkenyl aryl iodonium triflates (alkenyl group transfer for synthesis of trisubstituted alkenes), and aryl heteroaryl ethers. " Improved nickel-catalyzed cross-coupling conditions between oz-rto-substituted aryl iodides-nonaflates and alkyl-zinc iodides in. solution and in the solid phase have been defined. ... 

Another synthetically useful reagent of this type is 5,5-dimethyl-l,3-cyclohexanedione phenyliodonium ylide (781) (Scheme 3.308), a relatively stable iodonium ylide synthesized by condensation of PhI(OAc)2 with dimedone under basic condition [1060,1061]. Under catalytic, thermal, or photochemical conditions, ylide 781 serves as an excellent carbenoid precursor the transfer of such a carbenoid moiety to a suitable... 

As previously mentioned, oxidative addition of iodonium compounds to Pd(II) or Pt(II) centers provides one of the most effective pathways to M(IV) compounds. Canty [59] applied this method to the synthesis of Pt and Pd(IV) alkynyl derivatives 23 (Eq. (2.6)). To avoid decomposition of the unstable Pd(lV) complex, the reaction of the Pd(ll) complex 6 with the iodonium reagent needs to be carried out at low temperature over a long period (—SC C/l week). Szabo [60] has carried out density functional theory (DFT) calculations to model the addition of alkynyl- and aryliodonium compounds to the Pd pincer complex, and compared these processes with the oxidative addition of aryl iodides (Figure 2.2). Both alkynyl and aryl transfer... 

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