Intramolecular Reaction of a Phenonium Ion. Novel Lactonization of 4-Aryl-5-tosyloxypentanoates and 4-Aryl-5-tosyloxyhexanoates Concomitant with a Phenyl Rearrangement<sup>1</sup>
of the aromatic ring on the reactivity, it was found that the reaction proceeded via a phenonium ion. This finding was supported by the stereochemical results for the lactonization of opticalactive 1. Silica gel-promoted lactonization of 1 gave only gamma-lactone 2, whereas that of 3 afforded gamma-lactone 4 and delta-lactone 5. These lactonizations proved to be kineticallycontrolled. On the other
Lactonization of methyl 4-aryl-5-tosyloxy hexanoate 3 via a phenonium ion gave γ-lactone 4 selectively under thermodynamical conditions while it afforded δ-lactone 5 preferentially under kinetic conditions.