The Transformation of Cyclic Alcohols into Cyclic Acetals through a New Oxygen Atom Insertion by Photolysis in the Presence of Lead Tetraacetate and Iodine

Article abstract of DOI:10.1246/bcsj.60.1071

Photolysis of the hypoiodites of steroidal cyclic homoallyl alcohols such as cholesterol and of cyclic alcohols such as 5α-androstan-17β-ol generated in situ in bnezene with three molar equivalents each of lead tetraacetate and iodine was found generally to result in the unprecedented formation of corresponding lactol acetates in yields up to 66percent.The lactol acetates are readily hydrolysed to lactols in most cases during their isolation and lactols are isolated products.Thus, cholesterol gave 4-oxa-A-homocholest-5-en-3-ol and its acetate in a 53percent yield.The products differ considerably from those reported by us after the photolysis of the hypoiodites by using mercury(II) oxide and iodine as the reagents for generating the hypoiodites; they also differ from those in the oxidation of the steroidal alcohols with lead tetraacetate alone.The photolysis of the hypoiodite of 2,2-dimethyl-5β-cholestan-3-ol was found to lead to the formation of an anomaluos lactol, 2α-iodomethyl-2β-methyl-4-oxa-A-homo-5α-cholestan-4ξ-ol together with normal lactol.We discuss the paths of the formation of the lactol acetates involving β-scission of the alkoxyl radicals.A new process was found in the photolysis of 2-indanol hypoiodite in the presence of lead tetraacetate and iodine.Our previously suggested pathways to the formation of 3α,5-epoxy-6-iodo-4-oxa-A-homo-5α-cholestanes and 3-formyloxy-2-iodo-2,30seco-A-norcholest-5-ene in the photolysis of cholesterol hypoiodite in the presence of mercury(II) oxide and iodine were supported by the results of the photolysis of 4-oxa-A-homocholest-5-en-3-ol hypoiodite in the presence of mercury(II) oxide and iodine were supported by the results of the photolysis of 4-oxa-A-homocholest-5-en-3-ol hypoiodite in the presence of mercury(II) oxide and iodine.