ATOM TRANSFER CYCLIZATION OF SIMPLE HEXENYL IODIDES. A CAUTION ON THE USE OF ALKENYL IODIDES AS PROBES FOR THE DETECTION OF SINGLE ELECTRON TRANSFER PROCESSES
The trialkyltin initiated isomerization of 1-iodo-5-hexene to (iodomethyl)cyclopentane is reported.Rapid and reversible iodine atom transfer between alkyl radicals is the key chain transfer step.The results suggest an important caution in the use of hexenyl iodides as SET probes: a good mechanism exists whereby the yield of rearranged products may be much greater than the amount of radicals produced by the reaction under study!
Lithium-Iodine Exchange Mediated Atom Transfer Cyclization: Catalytic Cycloisomerization of 6-Iodo-1-hexenes
Treatment of 6-iodo-1-hexene (1) in a variety of solvent systems with either MeLi or PhLi at room temperature or above effects clean cycloisomerization of 1 to (iodomethyl)cyclopentane (4). This novel transformation, which is mediated by rapid and reversible lithium-iodine exchange processes, most likely involves the following discrete steps: (i) generation of 5-hexenyllithium (2) from 1 by exchange with MeLi or PhLi, (ii) irreversible cyclization of 2 to give (cyclopentylmethyl)lithium (3) and (iii) virtually complete conversion of 3 to (iodomethyl)cyclopentane (4) via a highly favorable lithium-iodine exchange equilibrium. The isomerization sequence 1 → 4 has been found to be effectively catalytic in PhLi when conducted in hydrocarbon-ether solvent mixtures at room temperature.
Bailey, William F.,Carson, Matthew W.
p. 361 - 365
(2007/10/03)
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