Himachalane, Longifolane

An X-ray crystallographic analysis of the p-bromobenzoate of (-1-)-allohimachalol, a constituent of the essential oil of Cedrus deodara Loud., has resulted in a slight revision of its stereochemistry to (224).  

A long standing mechanistic problem has been the route by (-t-)-longifolene (225) undergoes the acid-catalysed rearrangement to (-)-isolongifolene (232). Initially a mechanism was proposed in 1964 by Ourisson which was attractive especially in the economy of the number of steps (225)-(232). However, in 1967 Berson and co-workers ° pointed out that one of the steps, (227) - (228), involved an 2,3-methyl migration which lacked precedent in simpler 

Sukh Dev, B. Tagle, J. Telser, and J. Clardy, Tetrahedron Lett., 1980, 21, 325. 

A neat synthesis of a- and /S-panasinsene (255) has been described which incorporates an intramolecular variant of the cuprous triflate-catalysed photocycloaddition of the allylic alcohol (253) to afford (254).Oxidation of (254), followed by treatment with methyl-lithium and dehydration yielded a mixture 

Gatilov, Zh. V. Dubovenko, and V. A. Pentegova, Khim. Prir. Soedin. (Engl. Transi), 1979, 572. 

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Chart 20. Himachalanes, longifolanes, longipinanes, and sativanes found in the Hepaticae... 

Along with longifolane- and longipinane-types sesquiterpenes, (-h)-a-himachalene (436), (—)-P-himachalene (437) and (-h)-y-himachalene (438) have been isolated from Scapania undulata (2, 223). All himachalanes isolated are antipodal to those obtained from higher plants. 

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