Sesquiterpenes cycloisomerization reaction

Trost BM, Haffner CD, Jebaratnam DJ, Krische MJ, Thomas AP (1999) The Palladium-Catalyzed Enyne Cycloisomerization Reaction in a General Approach to the Asymmetric Syntheses of the Picrotoxane Sesquiterpenes. Part. I. First-Generation Total Synthesis of Corianin and Formal Syntheses of Picrotoxinin and Picrotin. J Am Chem Soc 121 6183... 

FIGURE 7.6 Cycloisomerization reactions and their biosynthetic correlation with sesquiterpene synthases. 

The close relationship of cyclization modes existed in sesquiterpene biosynthetic machinery, with those presented by the metal-catalyzed cycloisomerizations, justify the vast amount of reports on total synthesis of sesquiterpenes, in which the utilization of enyne or diene cycloisomerizations are the key components of their synthetic strategy. This chapter is intended to cover only selected examples on the topic. Special concern is given on covering catalyzed reactions, which are triggering different cyclization modes, only for the construction of sesqniterpene core strnctnres. Assuredly, cycloisomerization reactions are powerfnl tools in providing also other classes of secondary metabolites, as complex terpenoids and alkaloids, in which the readers are referred to more general reviews on the topic [26,30]. 

The examples presented in this subchapter represent only a selected portion of the vast amount of literature publications highlighting the ability of cycloisomerization reactions to built structural diversity within the class of sesquiterpenoids. As the reaction mechanisms are refined and more things are currently known not only from palladium cycloisomerization chemistry but also from other unique pi-metals like gold and platinum, more impressive cascades are expected to flourish the chemical literature. Although cycloisomerization reaction is counting more than four decades from its concept discovery, we are convinced that it will stiU remain one of the best atom-economical methods for the construction of structurally comphcated natural products as those contained in the unlimited sesquiterpene family. 

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