Chemistry of hop constituents. Part XXXIV. Methylation of some hop resins

Abstract

The hop resins colupulone and cohulupone have been methylated using diazomethane and methyl iodide. O-Methylation was obtained with diazomethane, colupulone giving mainly 6-isobutyryl-5-methoxy-2,2,4-tri-(3-methylbut-2-enyl)cyclohex-4-ene-1,3-dione, together with a number of minor products probably corresponding to the many enol forms possible. Cohulupone gave a mixture of four mono-O-methyl derivatives corresponding to the four possible mono-enolic forms. Methyl iodide methylation of colupulone gave 5-hydroxy-4-isobutyryl-2-methyl-2,6,6-tri-(3-methylbut-2-enyl)cyclohex-4-ene-1,3-dione, existing as the two possible enol chelates. Methyl iodide methylation of cohulupone gave no recognisable products.