SKELETAL REARRANGEMENT OF THE DEHYDROABIETIC ACID-DERIVATIVE

Methyl 7-oxo-5,8,11,13-abietatetraen-18-oate was reduced with sodium borohydride in the presence of cerium(III) chloride heptahydrate to give the corresponding 7-hydroxy compound, which was rearranged into methyl 7-isopropyl-1,10-dimethyl-1,2,3,4-tetrahydroanthracene-1-carboxylate (14) possessing a rearranged linear abietane skeleton, by a treatment with boron trifluoride etherate. The reduction of 14 with lithium aluminum hydride afforded 7-isopropyl-1,10-dimethyl-1,2,3,4-tetrahydroanthracene-1-methanol (15). This was further converted into 7-isopropyl-1,1,10-trimethyl-1,2,3,4-tetrahydroanthracene. The mesylate of 15 was also rearranged into 2-isopropyl-5,9-dimethyl-7,8-dihydro-6H-cyclohepta[b]naphthalene, possessing a seven-membered A ring.