Abstract
Oxy-functionalization of cholesteryl acetate (1a) occurred, giving 3β-acetoxy-5, 6-epoxycholestane (2a), 3β-acetoxycholest-5-en-7-one (3a), 3β-acetoxycholest-5-en-7-ol (4a), and an unidentified product (5), when 1a was oxidized by a system consisting of Fe (acac)3 and the hydroperoxide of an unsaturated long-chain fatty acid (LH) such as oleic, linolic, or linolenic acid (Table I). The epoxidation of stilbene by the same system was found to be non-stereospecific. These results and the fact that the reaction in this system was inhibited by a radical scavenger (BHT) were fairly compatible with those obtained with the Fe (acac)3-tBuOOH system, which is assumed to generate oxy and peroxy radicals. Autoxidation of 1a and cholesterol (1b) in the presence of Fe (acac)3 and LH proceeded after a time-lag of several hours and was also inhibited by BHT. The marked stereoselectivity of β-epoxidation (β/α+β=0.72) and the extent (about 30-40%) of allylic oxidation in the autoxidation were in fair agreement with those found for 1a in the Fe(acac)3-LOOH system (Table II). Autoxidation of stilbene in the presence of Fe (acac)3 and LH also led to non-stereospecific epoxidation. Thus, the autoxidation of cholesterols (1a and 1b) in the Fe (acac)3-LH system was assumed to be a radical reaction in which LOO·and LO·are the attacking species.
