A biomimetic synthesis of hitorins A and B was
achieved based on our modified biosynthetic proposal. In our synthesis, a
radical cascade reaction between an alkoxy radical, generated from a
hydroperoxide, and a monoterpene (+)-sabinene renders the tetrahydrofuran ring
of hitorins A and B. In addition, experimental results supported that the
oxidative cleavage of the tetrasubstituted olefin in a key intermediate is via
a radical oxidation cascade followed by a Grob fragmentation.<br>
The isomerization of diterpene epoxides on active neutral alumina has established the existence of new rearrangements of the diterpene skeleton. Methyl 8,14β-epoxysandarcopimarate leads to bicyclic diterpene compounds by a Grob fragmentation, to derivatives of cleistanthane by a 1,2 migration of the vinyl substituent, as well as to one cycloditerpene compound. The 7,8 (or 8,9) derivatives of methyl isopimarate lead essentially to hydroxyolefins formed by a bifunctional acid–base mechanism at the alumina surface. [Journal translation]
Biomimetic Synthesis of Hitorins A and B via an Intermolecular Alkoxy Radical-Olefin Coupling Cascade
