IDENTITY OF THE CHAIN-CARRYING SPECIES IN HALOGENATIONS WITH BROMOARYLALKOXYIODINANES AND CHLOROARYLALKOXYIODINANES - SELECTIVITIES OF IODINANYL RADICALS

The free-radical halogenation of substituted toluenes by haloiodinanes 2a-b and 3a-b in benzene solvent is highly selective for benzylic hydrogens. The process involves cyclic iodinanyl radicals, except in the case of 3b, which appears to react via a bromine atom chain. The essentially identical values of p+ for 2a (-1.46) and 2b (-1.48) are consistent with there being a common chain-carrying species for both bromination and chlorination. Identical p+ values were not observed for 3a (-1.31) and 3b (-1.55 vs. Br, -1.58). Such iodinanyl radicals, unlike those derived from phenyliodine dichloride, are constrained to a C-l-O angle far smaller than 180°, allowing an opportunity to study the effects of bending on radical selectivities. The intermediacy of iodinanyl radicals in free-radicals chlorinations is further supported by evidence from photoinitiated reactions of 2a and 3a with 2, 3-dimethylbutane. Comparisons of selectivities with those determined in other studies show that chlorine atoms are not involved. The allylic chlorinations of cis- and trans-2-butenes by 2a and 3a were studied and found to be selective, high-yield reactions which give little or no addition to the carbon-carbon double bond. © 1979, American Chemical Society. All rights reserved.