Iodonium salts, cross-coupling

Iodo dimethyl amido complexes, with Ti(IV), 4, 331-332 Iodonium salts, cross-coupling with lead reagents, 9, 413 Ionic addition reactions, mechanisms, 1, 101 Ionic bis(isonitrile) complexes, liquid crystals, 12, 280 Ionic character, organometallic compound dn configuration,... 

The alkenyl(phenyl) iodonium salt 725 undergoes the facile cross-coupling with vinylstannane to form the conjugated diene 726[594]. 

Palladium-catalysed cross-coupling of organotellurium compounds with hypervalent iodonium salts... 

Scheme 16 Cross-coupling reaction of Ar3BiX2 with iodonium salts...

The reaction of 4-methoxyphenyl-, 2-thienyl- and styryl-iodonium salts with triarylbismuth(V) compounds was efficiently catalyzed by PdCl2 in MeCN at room temperature to afford cross-coupling products in good yields (Scheme 16) [33]. There is no mention about possible homo-coupling side-products. 

A similar cross-coupling reaction between triarylbismuth(V) compounds and aryl-, heteroaryl-, or styryltributylstannanes smoothly proceeded under the same reaction conditions as those for the iodonium salts (Scheme 17) [34]. Homocoupling side products were not mentioned. 

Furo[2,3- ]pyridines can be synthesized from alkynylpyridones and iodonium sources (Scheme 31) <20060L1113>. Iodine proved to be much more effective at promoting the iodocyclization reaction than other iodonium sources (ICl, A -iodosuccinimide (NIS)). The pyridinium triiodide salt, 104, can be converted into the corresponding pyridinone by treatment with an external source of iodide. In a variation of the reaction, a one-pot synthesis of the furopyridine derivatives 105 can be achieved, with overall yields of 79-92%, by treatment with iodine followed by sodium iodide without isolation of the triiodide salt. Another similar one-pot synthesis involves 3-iodo-2-pyridones, terminal alkynes, and organic halides in a series of two palladium cross-coupling reactions (Equation 45) <20030L2441>. This reaction could also be carried out in a two-step sequence, but the overall reaction yields were typically improved for the one-pot method. 

Carbonylative cross-coupling of various iodonium salts bearing transferable aryl, heteroaryl, alkenyl, alkynyl residues with phenylboronic acid takes place under mild conditions giving the respective ketones in high yields (Equation (16)). The yields of competing cross-coupling do not exceed 8%. 

A polyethylene glycol-polystyrene graft copolymer palladium catalyst has been used in allylic substitution reactions of allyl acetates with various nucleophiles in aqueous media.58 Another polymer-bound palladium catalyst 40 was developed and used in a Heck coupling of allylic alcohols with hypervalent iodonium salts to afford the substituted allylic alcohols as the sole products under mild conditions with high catalytic efficiency.59 The same polymer-bound palladium catalyst has also been used for Suzuki cross-coupling reactions.60... 

Organotin compounds can be effectively used as substrates in the palladium-catalyzed cross-coupling reactions of alkenyliodonium salts [66,67]. For example, the reaction of alkenyliodonium triflate 84 with 5-stannylated uracil 83 proceeds smoothly to provide cross-coupled products 87 in moderate yield. The same products 87 are obtained in almost quantitative yield in the palladium-catalyzed cross-coupling of uracil iodonium triflate 85 and vinyltin 86 (Scheme 39) [67]. 

It is assumed that the mechanism of the palladium-catalyzed cross-coupling reactions of iodonium salts involves the initial oxidative addition step, followed by ligand coupling at the iodine and then at the palladium centers analogously to the mechanism shown in Scheme 31 [63,66]. 

Cross-coupling reactions of iodonium salts with terminal alkynes or organostannanes can also be effectively catalyzed by Cul, MnCl2 4H20, or Ni(acac)2 [56,58,103,104]. 

For Pd-catalyzed cross-coupling reactions the organopalladium complex is generated from an organic electrophile RX and a Pd(0) complex in the presence of a carbon nucleophile. Not only organic halides but also sulfonium salts [38], iodonium salts [39], diazonium salts [40], or thiol esters (to yield acylpalladium complexes) [41] can be used as electrophiles. With allylic electrophiles (allyl halides, esters, or carbonates, or strained allylic ethers and related compounds) Pd-i73-jt-allyl complexes are formed these react as soft, electrophilic allylating reagents. 

Reductive coupling of iodonium salts catalysed by a palladium-zinc system also produced biaryls in good yield [38]. Also very effective was the palladium-catalysed cross-coupling of iodonium salts with sodium tetraphenylborate in water [39]. The reaction of 3-indolyl phenyliodonium trifluoroacetate with several alkyl and aryl lithium reagents gave 3-substituted indoles [40] ... 

Cross-coupling reactions between iodonium salts and organolead reagents can be catalyzed by palladium (Equation (107)).121 These reactions required 2 equiv. of base. In this system, homocoupling of the reagent could not be completely suppressed (Ar-Ar, 10-20%), and the reported yields for the products of the heterocoupling pathway (Ar-Ar ) were moderate (62-75%). 

While organic chlorides, bromides, and iodides are still the most common substrates, recently the scope has been expanded to include organic fluorides, nitriles, ethers, triflates, phosphates, iodonium salts, and substrates with various chalconide-leaving groups. Of the different cross-coupling reactions covered in this article, the Kumada Corriu protocol has been the least reviewed. However, the topic has been covered in recent historical treatments. ... 

Diaryliodonium salts represent the most stable and well-investigated class of iodonium salts. Their chemistry was extensively covered in several reviews [854,855,860]. The most important and synthetically useful reactions of diaryliodonium salts include the following the direct electrophilic arylation of various nucleophiles, transition metal mediated cross-coupling reactions and reactions involving generation and trapping of the benzyne intermediates. 

AUcynylstannanes can cross-couple with a variety of other functional groups employing the Stille protocol. Couphng to acyl chlorides is a well-known procedure that affords aUcynylketones in respectable yields. Other reports include alkynyltin cross-couplings with a-haloethers and a-halocarbonyls, enol phosphinates and phosphonates, alkenyl(phenyl)iodonium salts, alkynyl halides, and allyl hahdes (Table 9.18). Alkynylstannanes have also been shown to cross-couple with iron halides under the Stille conditions to effectively form iron-carbon bonds. 

The cross-coupling reactions of organoboronic acids and carbon monoxide with hyper-valent iodonium salts affords unsymmetrical ketones (Scheme 30). The reaction proceeds smoothly at room temperature and in most cases completes within 0.5 h. Aryl-, alkenyl-, and alkynyliodonium salts react with arylboronic adds in the presence of 0.5% of Pd(PPh3)4 and 1.2 equiv of K2CO3 in DME to provide unsymmetrical aromatic ketones in high yields (Scheme 30). Phenylboronic acid dimethyl ester can be utilized as efficiently as phenylboronic acid. In most cases, a small amount of the direct crosscoupling product (R—Ph, less than 7-8%) is produced. 

Diaryliodonium salts can be used in cross-coupling with boronic acids or sodium tetraphenylborate in place of aryl halides. This reaction can be performed in water in the presence of catalytic amounts of PdCla. At 80°C both the aryl groups of the iodonium salt are involved. The addition of base is required to enable the transfer of all four phenyl groups of PlijBNa [47] ... 

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. 

Cross-Coupling Reaction Using 2-Fluoro-l -halo-1 -alkenes or (2-Fluoro-l-alkenyl)iodonium Salts... 

In the transition metal catalyzed cross-coupling reaction, the (2-fluoroalkenyl) iodonium salt has two reactive sites, a phenyl group and a fluoroalkenyl group. 

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