1956 I. L. Finar II. viii. 252 Bicyclic monoterpenes contain a six-membered ring and a three-, four-, or five-membered ring.
1978 A. J. Birch in (Ciba Symposium) 6 A similar cyclization to a six-membered ring from the C20-precursor geranyl-geranyl pyrophosphate would not yield this group.