Photoinduced Molecular Transformations. Part 154. On the Mechanism of the Formation of the 5-Iodopentyl Formate in the Photolysis of Cyclopentanol Hypoiodite in Solution in the Presence of Mercury(II) Oxide-Iodine.

Article abstract of DOI:10.1016/S0040-4020(01)89319-4

(18)O-labelling experiments established that the formation of 5-iodopentyl formate in the photolysis of cyclopentanol hypoiodite in the presence of excess mercury(II) oxide-iodine in benzene involves the following pathway: a) a β-scission of a cyclopentyloxy radical to rearrange to a primary 5-oxopentyl radical, which generates the corresponding carbocation by a metal ionassisted one-electron oxidation; b) an intramolecular addition of the 5-oxopentyl cation to the formyl oxygen to generate a tetrahydropyranyl cation; c) a combination of the tetrahydropyranyl cation with diiodine oxide (I2O) to form a lactol hypoiodite; d) generation of a carbon-centred radical by a selective β-scission of a carbon-carbon bond of an alkoxyl radical generated from the lactol hypoiodite; e) abstraction of an iodine by the carbon-centred radical from an iodine molecule to form the 5-iodopentyl formate. 5-Iodopentyl formate is also produced by prolonged irradiation of a solution of 5-iodopentanal in the presence of mercury(II) oxide and iodine in benzene with Pyrex-filtered light.The formate in this case should be formed through the generation of the 5-oxopentyl cation (mentioned above) by mercury-assisted ionization of its carbon-iodine bond, followed by the same pathway as that mentioned above.