Abstract: The present invention relates to a method for the preparation of dronabinol ((6aR-trans)-6a,7,8,10a-tetrahydro-6,6,9-trimethyl-3-pentyl-6H-dibenzo[b,d]pyran-1-ol, ?9-tetrahydrocannabinol (?9-THC)) from cannabidiol (CBD) by cyclization of cannabidiol (CBD) (2-[1R-3-methyl-6-(1-methylethenyl)-2-cyclohexene-1-yl]-5-pentyl-1,3-benzoldiol) to ?9-THC. The method according to the present invention is characterized in that cannabidiol (CBD) (B) is present in an organic solvent and cyclized to ?9-THC in the presence of a molecular sieve while being heated. It was found out that, in the method of the present invention, the molecular sieve not only has the previously mentioned drying properties, but also exhibits strong catalytic properties which are important in this reaction. Normally, cyclizations carried out in the presence of a Lewis acid catalyst only are distinctly slower and the ?9-THC yield is lower than in cyclizations carried out in the present of a molecular sieve.

Abstract: The present invention relates to a method for the preparation of dronabinol ((6aR-trans)-6a,7,8,10a-tetrahydro-6,6,9-trimethyl-3-pentyl-6H-dibenzo[b,d]pyran-1-ol, ?9-tetrahydrocannabinol (?9-THC)) from cannabidiol (CBD) by cyclization of cannabidiol (CBD) (2-[1R-3-methyl-6-(1-methylethenyl)-2-cyclohexene-1-yl]-5-pentyl-1,3-benzoldiol) to ?9-THC. The method according to the present invention is characterized in that cannabidiol (CBD) (B) is present in an organic solvent and cyclized to ?9-THC in the presence of a molecular sieve while being heated. It was found out that, in the method of the present invention, the molecular sieve not only has the previously mentioned drying properties, but also exhibits strong catalytic properties which are important in this reaction. Normally, cyclizations carried out in the presence of a Lewis acid catalyst only are distinctly slower and the ?9-THC yield is lower than in cyclizations carried out in the present of a molecular sieve.