Synthesis of (-)-11 Hydroxy-delta8-6a, 10a-trans-tetrahydrocannabinol

When (?)-Δ⁸-6a, 10a-trans-THC (THC = Tetrahydrocannabinol), in the form of its diacetate, was irradiated in the presence of oxygen and a sensitizer, followed by reduction with NaBH₄, three allylic alcohols were formed: (?)-8α-and (?)-8β-hydroxy-Δ^9,11-THC (proportion 3:1) and (?)-9α-hydroxy-Δ^7,8-THC. Acetylation of the epimeric 8-hydroxy-compounds with Ac₂O/pyridine gave the corresponding diacetates. When (?)-Δ⁸-6a, 10a-trans-THC, in the form of its tetrahydropyranyl derivative, was heated with m-chloroperbenzoic acid, the two epimeric 8,9-epoxides were formed in equal amounts. These compounds, on treatment with butyllithium, afforded (?)-8α- and (?)-8β-hydroxy-Δ^9,11- 6a, 10a-trans-THC-tetrahydropyranylether. After removing the protecting group and treatment with Ac₂O/pyridine the same diacetates, as formed by photooxygenation of (?)-Δ⁸-THC-acetate, were obtained as a 1:1-mixture. On heating these epimeric diacetates to 290° they underwent allylic rearrangement to (?)-11-acetoxy-Δ⁸-THC-acetate. From this (?)-11-hydroxy-Δ⁸-6a, 10a-trans-THC was obtained by treatment with LiAlH₄.