Abstract
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.
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