Terpenes hydrogen rearrangements

Hydrogen fluoride adds to more complex molecules, such as unsaturated steroids, to give fluorinated derivatives [/, 8] Low temperatures and inert diluents, such as tetrahydrofuran or methylene chloride, are generally employed. With bicyclic unsaturated terpenes, rearrangements often accompany addition to the double bond [/]. 

The photo-cycloaddition of ethylene to 3-alkoxy chromones such as 315 has been applied to the synthesis of marine sesquiterpene filiformin and congeners (Scheme 43) <1996JOC4391>. Tandem [2+2] 7i-photo-cycloaddi-tion and y-hydrogen abstraction provided tetracyclic intermediate 316 which was converted to terpene 317 by subsequent oxetane ring reduction and acid-catalyzed rearrangement. 

Catalytic transformations of terpenes are well documented [213-215], comprising a wide variety of reactions hydrogenation, dehydrogenation, oxidation, hy-droformylation, carbonylation, hydration, isomerization and rearrangement, and cyclization. 

The addition of hydrogen fluoride across double bonds in unsaturated bicyclic terpenes is accompanied in many cases by rearrangements. Hence, hydrofluorination of camphene with... 

Synthesis of Camphor.— The relationship of camphor to pinene, the terpene present in turpentine, is of especial interest and importance in connection with its synthesis. Pinene is the unsaturated di-cyclic terpene related to the saturated di-cyclic terpene pinane (p. 823). In both of these terpenes the di-cyclic arrangement is different from that in camphane and Bornylene in that the isopropyl group in forming the secondary cycle joins the meta carbons instead of the para. Now pinene, by addition of hydrogen chloride, forms a hydrochloride which has been referred to as artificial camphor. This hydrochloride is identical with the hydrochloric acid ester of Bomeol and may be converted into Bomeol by hydrolysis. Now as Bomeol can be oxidized to camphor we may thus obtain true synthetic camphor from pinene. The reactions, involving an intermediate product and then rearrangement of the secondary cycle in pinene, are as follows ... 

Rearrangement of the primary halide product (Wagner-Meerwein rearrangement) occurs when HC1 or HBr is added to bicyclic terpenes, especially in solvents of high dielectric constant and when an excess of hydrogen halide is used. For the mechanism see Gould.18d... 

CHAlUHGtl Humulene and a-caryophyllene alcohol are terpene constituents of carnation extracts. The former is converted into the latter hy acid-catalyzed hydration in one step. Write a mechanism. (Hint The mechanism includes cation-induced double-bond isomerization, cyclizations, and rearrangements that may involve hydrogen and alkyl-group migrations. Two of the intermediates in the mechanistic sequence are shown five carbon atoms are identified by starts to help you track their positions through the process.)... 

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