Novel synthesis of (−)‐trans‐Δ⁹,¹¹‐tetrahydrocannabinol

Addition of hydrogen chloride gas to a solution of Δ 8 ‐tetrahydrocannabinol in dry dichloromethane at ‐60° in the presence of zinc chloride results in the formation of a higher concentration of 9‐α‐chlorohexa‐hydrocannabinol (75%) than the thermodynamically more stable 9‐β‐chlorohexahydrocannabinol (25%). The two isomers can be separated by reverse‐phase hplc. Elimination of hydrogen chloride from 9‐α‐chlorohexa‐hydrocannabinol using potassium t ‐amylate under anhydrous conditions gives exclusively Δ 9,11 ‐tetrahydrocannabinol in overall yield of 65%.