A simple synthesis of trans-hexahydrocannabinol via an o-quinonemethide in protic solvent was established. The methanol solution of coupling product of a resorcinol derivatives and citronellal was refluxed in the presence of p-methylbenzenesulforic acid as an catalyst, the deprotection of phenols, production of o-quinonemethides and intramolucular Diels-Alder cycloaddition reaction took place in one step, in 93%～95% yield.

Key words: o-quinonemethide, Diels-Alder reaction, trans-hexahydrocannabinol