Synthesis and acid- and base-promoted ring opening of polycarbocyclic oxiranes

Acid promoted ring opening of 1 alpha,4 alpha,4a alpha,9a alpha-tetrahydro-2 beta-3 beta-epoxy-1,4-methanoanthracene-9,10-dione and the corresponding 2-methyl derivative (i.e., 3a and 3b, respectively) afforded 4a and 46 in 26% and 49% yield, respectively. Similar results were obtained when a solution of either 3a or 3b in aqueous acetone was reacted with Na2CO3 at ambient temperature for 2 days. However, reaction of 3b with aqueous methanolic NaOH (ambient temperature, 7 days) produced a small quantity of 46 along with a novel pentacyclic diketone, 6b (44% yield). Finally, acid promoted ring opening of 1 alpha,4 alpha-dihydro-4a alpha,9a alpha-epoxy-1,4-methanoanthracene-9,10-dione (12) resulted in extensive skeletal rearrangement of the substrate, thereby affording 14 in low yield. (C) 1998 Elsevier Science Ltd. All rights reserved.