A-Alaskene

Organic molecnles in which one carbon atom is common to two rings are called spirocyclic componnds. The simplest spirocyclic hydrocarbon is spiropentane, a product of laboratory synthesis. More complicated spirocyclic hydrocarbons not only have been synthesized bnt also have been isolated from natnral sources. a-Alaskene, for example, occurs in the fragrant oil given off by the needles of the Alaskan yellow cedar one of its carbon atoms is common to both the six-membered ring and the five-membered ring. 

Acorone (166), a sesquiterpene diketone isolated from the essential oil of roots of Acorus calamus, was the first spirosesquiterpenoid to be characterized, with the carbon skeleton of cation 158. At present several compounds of this class are known and an extensive review has been published (267). Hydrocarbons (e.g., y-acoradiene = a-alaskene, 167) and alcohols (e.g., a-acorenol, 168) directly derivable from the spiro-cation 159 have been isolated from wood of Juniperus... 

Barbilophozia barbata elaborates (—)-a-alaskene (31) whose structure has been established by comparison of the spectral data with those of an authentic sample (5, 6). 

It is clear from these and previous results obtained over the past two or three years that the spiro-sesquiterpenes provide an important link between certain monocyclic and tricyclic sesquiterpenes. This is further exemplified by the recent work of Andersen and SyrdaP who have now reappraised the absolute stereochemistries of (-)-a- (137) and (- )-/3-alaskene (138). It now appears that 5-acoradiene, isolated by Hirose et is, in fact, (-I-)- -alaskene. Andersen and Syrdal also made the interesting observation that phthalic anhydride dehydration of the diols derived from iso-acorone (139) gave rise to small amounts of (-f )-a-cedrene (126 R = Me) and (— )-2-epi-a-cedrene (136). Subsequently these authors found that (-t- )-nerolidol (140) and a number of its derivatives undergo acid-catalysed cyclization to a mixture of a- and -bisabolenes (141), of which the... 

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