The synthesis of some novel deoxyhumulone analogues. Observations on the air-oxidation of 2′,4′,6′-trihydroxy-3′-isopentyl-5′-(3-methylbut-2-enyl)isovalerophenone and its corresponding humulone derivatives
Abstract
Two novel analogues of natural deoxyhumulone have been synthesised: (a) with the 3-methylbutanoyl side chain replaced by benzoyl, and (b) with the dimethylallyl substituents replaced by the cycloheptylidene analogues. Oxidation of these with air gave the corresponding humulones. Modification of these syntheses afford the two half-hydrogenated deoxyhumulone analogues, 2,4,6-trihydroxy-3-isopentyl-5-(3-methylbut-2-enyl)benzophenone and 2′,4′,6′-trihydroxy-3′-isopentyl-5′-(3-methylbut-2-enyl)isovalerophenone. Air-oxidation of the latter compounds gave in each case two isomeric humulones. Each pair of humulones was oxidised further, competitively, and the progress of the oxidation followed by 1H n.m.r. spectroscopy. The results indicated a preferential oxidation rate for the isomers containing an unsaturated side chain at C-5 rather than at C-3.
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