Phenylation, hypervalent iodine compounds

AT-Substituted amidines 74 are transformed via the carbodiimide intermediate 75 into urea derivatives 76 as shown in Scheme 34 [141]. This reaction has been performed with a variety of aliphatic and aromatic substituents and in addition to (diacetoxyiodo)benzene 3 other hypervalent iodine compounds can also be used for this rearrangement. Phenyl substituted amidines 74 (R = Ph) can lead to cyclized products of type 77. 

Treatment of aryl-substituted alkenes with hypervalent iodine compounds can lead to the formation of phenyliodinated intermediates, which can be stabilized by the aryl substituent via the formation of phenonium ions. Subsequent nucleophilic attack might then lead to rearranged products. This behavior can be nicely seen by comparing the unsaturated carboxylic acids 78 in their reaction with (diacetoxyiodo)benzene 3. The substrate 78a without the phenyl substituent is cyclized to the phenyliodinated intermediate 79, which is then attacked by the acetate under the formation of lactone 81 [142]. Substrate 78b is, however, then stabilized by the formation of an intermediate phenonium ion 80 and attack by the acetate is accompanied by a 1,2-phenyl migration and 82 is generated, Scheme 35 [143]. 

Alkynyliodonium ions, 1 and 2, are hypervalent iodine species in which one or two alkynyl ligands are bound to a positively charged iodine(III) atom. They are sensitive to nucleophiles, especially at the /1-carbon atom(s) of the alkynyl ligand(s), and for that reason, the isolation of stable alkynyliodonium salts generally requires the incorporation of nucleofugic anions. A list of known alkynyliodonium compounds (i.e. as of 4/1/94), containing 134 iodonium salts derived from 103 iodonium ions, and references (5-45) to their preparation and characterization are presented in Table 1. Among these compounds, alkynyl(phenyl)iodonium sulfonates and tetrafluoroborates are the most common, while alkynyl(alkyl)iodonium salts of any kind are unknown. 

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