Synthesis of cannabinoids by pyridine-catalysed citral–olivetol condensation: synthesis and structure of cannabicyclol, cannabichromen, (hashish extractives), citrylidene-cannabis, and related compounds
Citral condenses with olivetol in the presence of pyridine (1 mol) to give citrylidene-cannabis(III)(26%), cannabi-chromen (IV)(15%), its isomer (V)(3%) the bischromen (II)(6%), cannabicyclol (IX)(1%), its isomer (XV)(3%), and the bis-compound (XVI)(1·3%). Cannabichromen when heated with pyridine gives citrylidene-cannabis and cannabicyclol: the latter is also formed from cannabichromen under acid catalysis, and photochemically, in preparatively acceptable yields. Reasons for revising to (IX) the earlier structural proposal (VII) for cannabicyclo, are presented. Cannabichromen and cannabicycol are extractives of Cannabis(hashish).
Acid-catalysed reactions of citrylidene-cannabis, cannabichromen, and the citral-olivetol system are discussed. The information accumulated in this, and the preceding paper, is summarised in a scheme for pyridine- and acid-catalysed condensations of citral with resorcinols or phloroglucinols.