A Concise and Convenient Synthesis of <scp>dl</scp>-<i>proto</i>-Quercitol and <scp>dl</scp>-<i>gala</i>-Quercitol <i>via</i> Ene Reaction of Singlet Oxygen Combined with [2 + 4] Cycloaddition to Cyclohexadiene

Abstract

Photooxygenation of 1,4-cyclohexadiene afforded hydroperoxy endoperoxides 3 and 4 in a ratio of 88:12. Reduction of 3 with LiAlH(4) or thiourea followed by acetylation of the hydroxyl group and KMnO(4) oxidation of the double bond gave proto-quercitol 10b. Application of the same reaction sequences to 4 resulted in the formation of gala-quercitol 14. Quercitols were easily obtained by ammonolysis of acetate derivatives in MeOH. The outcome of dihydroxylation reactions were supported by conformational analysis.