The stereochemistry and absolute configuration of abienol

Abienol, the diterpenoid alcohol present in Abies oleoresinl-5 and in particular obtainable from the oleoresin of Abies balsamea (Canada b a l ~a m ) , ~ has been a s ~i g n e d ~-~ the structure (I) (without stereochemical implications).During a recent survey of optical rotation and structure in the bicyclio diterpenoid series,= it was observed that abienol had an unexpectedly high rotation.If simple molecular rotation differences are meaningful, then abienol (I) should have a rotation approximately equal to that of sclareol ( 11) ( [ M I , -15) plus biformene (IV) ([MI, f33) minus man001 (V) ([MI, +96); i.e, a molecular rotation of -78 units.Abienol in fact5 has [MI, f70 which led to the suggestion6 that abienol