Oxidation of deoxyhumulones with air. Evidence of divergent and sequential products from deoxyhumulones

Abstract

Air oxidations of the model deoxyhumulones 2′,4′,6′-trihydroxy-3′-methy!-5′-(3-methylbut-2-enyl)acetophenone (6), 2′,4′,6′-trihydroxy-3′-isopentyl-5′-(3-methylbut-2-enyl)acetophenone (12), and 2′,4′,6′-trihydroxy-3′,5′-di-(3-methylbut-2-enyl)acetophenone (7)(deoxyacetohumulone) have shown that besides the corresponding humulones, 8-acetyl-2,2,6-trimethylchroman-3,5,7-triol (10), 8-acetyl-2,2-dimethyl-6-isopentylchroman-3,5,7-triol (18), and 8-acetyl-2,2-dimethyl-6(3-methylbut-2-enyl)chroman-3,5,7-triol (20) respectively are formed competitively. For the model deoxyhumulones (6) and (12) which give rise to two isomeric humulones, in each case one of the latter compounds undergoes further oxidation discriminately, whilst deoxyacetohumulone (7) gives a low yield of the isohumulones (25) and evidence for formation of the epoxyisohumulone (23) is presented. The hydroxychroman (20) oxidises slowly in air to 2,3,7,8-tetrahydro-5-acetyl-7,7-dimethyl-2-(1-methyl-1-hydroxyethyl)furo[2,3-f]benzopyran-4,8-diol (24).