Efforts Toward the Synthesis of Maoecrystal V and Atropurpuran with the Discovery of Novel Skeletal Rearrangements

Abstract

Synthetic strategies and efforts towards two complex diterpene natural products, maoecrystal V and atropurpuran are described. Novel skeletal rearrangements that were observed during the travails of the latter are reported.

The first chapter describes efforts to synthesize the bioactive diterpenoid, maoecrystal V in enantiopure fashion starting from (+)-limonene oxide. An intramolecular Rh(II)-catalyzed C-H insertion reaction installed the tetrahydrofuran ring with requisite stereochemistry. The chemistry culminated with the installation of all desired atoms albeit with unsuccessful attempts to install the desired δ-lactone.

The last chapter presents efforts to make the fused double bicyclo[2.2.2]octane containing diterpene, atropurpuran. Initial attempts to forge the skeletal core of the system were proposed to use cascading [4+2] cycloaddition chemistry. After it became apparent that the first strategy would unlikely be successful, a slightly reworked strategy provided the first synthetically made fused double bicyclo[2.2.2]octane molecule in low yield. Then a major strategy shift to attempt to make desired ring system via cascading radicals generated from arylsulfonyl hydrazones, led to an unexpected skeletal rearrangement under neutral conditions. A few examples of this novel reaction are presented. A second unexpected reaction forming a tricyclic-azo-compound occurred when attempting to expand the scope of the first C-C insertion reaction.