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.

Abstract

18O-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 ion-assisted 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 (I 2O) 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 fight. 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.