Radical hypervalent iodine-mediated

The use of hypervalent iodine reagents in carbon-carbon bond forming reactions is summarized with particular emphasis on applications in organic synthesis. The most important recent methods involve the radical decarboxylative alkylation of organic substrates with [bis(acyloxy)iodo]arenes, spirocyclization of para- and ortho-substituted phenols, the intramolecular oxidative coupling of phenol ethers, and the reactions of iodonium salts and ylides. A significant recent research activity is centered in the area of the transition metal-mediated coupling reactions of the alkenyl-, aryl-, and alkynyliodonium salts. 

A radical cation is involved in the direct synthesis of chromans by an intramolecular oxidative cyclisation of 3-arylpropanols 32 brought about by a hypervalent iodine(III) reagent <04TL2293> and iodonium species catalyse the intramolecular arylation of alkenes which yields iodo-substituted chromans 33 <04JA3416>. 3-Allenylchroman-4-ols result from a one-pot reaction between salicylaldehydes and 1,4-dibromobut-2-yne in which the intramolecular cyclisation of the intermediate ether is mediated by In metal <04SL45>... 

In the presence of silicon Lewis acids, aryliodine bis(trifluoroacetate)s mediate efficient oxidative homocouplings of pyrroles and thiophenes to give 2,2 -bispyrroles and 2,2 -bisthiophenes, respectively [158]. The Lewis acids activate the hypervalent iodines (III) for single electron oxidation of the heteroarenes. The cation radicals thus generated add to the unreacted arenes to form the homocoupling products (Scheme 9.67). 

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