Rearrangement of terpenes

The conversion is thought to involve formation of the carboxonium ion (77) by protonation of the carbonyl oxygen, and subsequent protonation then occurs at the C-H bond. The resulting carboxonium-carbonium dication (78) possesses the maximum possible charge-charge separation for this bicyclic framework. Subsequently, an intermediate carboxonium-carbenium dication (79) is produced, which isomerizes to the tertiary -carbenium ion, and deprotonation provides the product enone (80). Similar distonic superelectrophiles are proposed in other rearrangements of terpenes in superacid.28... 

Among the various classes of natural products, perhaps none is as extensive as the collection of structures that derive ifom the union and rearrangement of terpene building blocks. Indeed, whether in the form of a relatively small compound such as pinene or a far more complex and biochemically relevant steroid hormone, these secondary metabohtes are ubiquitous throughout Nature. Despite their widespread presence, however, their structures are far from ordinary, as many possess molecular architectures so exotic that even the most inventive of chemists would have a hard time imagining them prior to their full structural elucidation. 

OURISSON, G. Molecular Rearrangements of Terpenes. Proc. Chem. Soc. (London) 1964, 274. 

Coates, R. M. Biogenetic-Type Rearrangements of Terpene. In Progress in the Chemistry of Organic Natural Products, Vol. 33 (Herz, W., H. Grisebach, and G. W. Kirby, eds.), p. 73. Wien-New York Springer. 1976. 

Coates, R. M., Biogenetic-type rearrangements of terpenes, Fortschr. Chem. Org. Naturst., 33, 73-220 (1976). 

Contents L. MINALE, G. CIMINO, S. DE STEFANO, and G. SODANO, Natural Products from Porifera - R. M. COATES, Biogenetic-Type Rearrangements of Terpenes - K. L RINEHART, JR., and L. S. SHIELD, Chemistry of the Ansamycin Antibiotics - A. FONTANA and C. TONIOLO, The Chemistry of Tryptophan in Peptides and Proteins -P. HEMMERICH, The Present Status of Flavin and Flavocoenzyme Chemistry - Author Index - Subject Index. 

Biogenetic-Type Rearrangements of Terpenes SbFs, SOgClF... 

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