Continuous-Flow Synthesis of Δ 9 -Tetrahydrocannabinol and Δ 8 -Tetrahydrocannabinol from Cannabidiol.

A challenging step in the preparation of tetrahydrocannabinol analogs is an acid-catalyzed intramolecular cyclization of the cannabidiol precursor. This step typically affords a mixture of products, which requires extensive purification to obtain any pure products. We report the development of two continuous-flow protocols for the preparation of (-)- trans -Δ 9 -tetrahydrocannabinol and (-)- trans -Δ 8 -tetrahydrocannabinol.