A NEW SYNTHESIS OF WALKERS COLUPULONE DEGRADATION PRODUCTS

The by-product in the reaction of ββ-dimethylacrylyl chloride with phloroglucinol has been shown to be 5-hydroxy-2,2,8,8-tetramethylbenzo[1,2- b:3,4-b′]dipyran-4(3H),10(9H)-dione. Sodium borohydride reduction gave 3,4,9,10-tetrahydro-2,2,8,8-tetramethylbenzo[1,2-b:3,4-b′]dipyran-5-ol, which was acylated to 3,4,9,10-tetra-hydro-6-isobutyryl-2,2,8,8- tetramethylbenzo[1,2-b:3,4-b′]dipyran-5-ol and then isomerised to its linear isomer, 3,4,6,7-tetrahydro-10-isobutyryl-2,2,8,8-tetramethylbenzo[1,2-b: 5,4-b′]dipyran-5-ol. The last-mentioned compounds were identical with authentic specimens obtained by degradation of colupulone with acid.