RESIN ACIDS .18. LITHIUM-AMMONIA REDUCTION OF SOME RESIN ACID ENONES

The reduction of 11-oxo-13β-abiet-8(9)-en-18-oate (3) with lithium-liquid ammonia afforded primarily the less stable B/C cis-fused methyl 11-oxo-8α,13β-abiet-8(9)-en-18-oate (5). Methyl 7-oxo-13β-abiet-8(9)-en-18-oate (10) gave quite unexpectedly the B/C cis-fused methyl 7-oxo-8β,9β,13β-abietan-18-oate (18b). The lack of parallelism between the reductions of these abietanes and their steroidal counterparts which undergo conversion into the more stable B/C trans system is ascribed to the absence of ring D which allows ring C of abietanes to assume conformations not permitted in the steroid series. The formation of 18b appears to result from protonation of the most stable carbanion intermediate rather than from overlap control. © 1969, American Chemical Society. All rights reserved.