Photo- and Thermally-induced Radical Rearrangement of 4,4-Dimethyl-5-cholesten-3β-ol Hypoiodite in the Presence of Mercury(II) Oxide and Iodine

Publisher Website
Google Scholar
Abstract
Irraidation of a benzene solution of hypoiodite of 4,4-dimethyl-5-cholesten-3β-ol (1) in the presence of mercury(II) oxide and iodine gave a mixture of products, from which 3α,5-epoxy-6β-iodo-A-homo-4-oxa-5α-cholestane (2%), 4,4-dimethyl-3-oxa-5-cholestene (3) (10%), and 4a,4a-dimethyl-3α,5-epoxy-A-homo-4-oxa-5α-cholest-6-ene (4) (4%) were isolated. The thermally-induced reaction on 1 conducted at 55–60 °C gave 3 and 4 in lower yields. The reaction with the use of lead tetraacetate-iodine reagent also gave a complex mixture, from which only 4 was obtained in 22% yield. The formation of 4,4-dimethyl-3-oxa-5-cholestene skeleton is parallel with the case of the photo- and thermally-induced reactions of hypoiodite of 3α,4,4-trimethyl-5-cholesten-3β-ol and appears to be particular with 5-cholesten-3β-ol bearing dimethyl groups at the C-4 under similar conditions. The formation is explained in terms of radical-induced decarbonylation of initially formed 4,4-dimethyl-2-formyl-3-oxa-5-cholestene.