Concise total synthesis of (±)-pisiferin

Enantioselective Total Synthesis of (-)-Rubriflordilactone B by a Bioinspired Skeletal Reorganization Approach

Rubriflordilactone B is a Schisandra bisnortriterpenoid with a unique 5/5/7/6/5/5-hexacyclic framework that includes a characteristic tetrasubstituted aromatic ring. Herein, we report a convergent, enantioselective total synthesis of this natural product by a bioinspired skeletal reorganization approach. Key transformations include a chelation-controlled [2,3]-Wittig-Still rearrangement to assemble the western cyclohexenyl fragment with complete diastereocontrol, a Cu(II)-catalyzed tandem acyloin acylation-Wittig olefin to build the eastern butanolide fragment, a Friedel-Crafts cyclization to construct the seven-membered ring, and an E1cB reaction/transesterification/oxa-Michael addition cascade to forge the pivotal 5/5-fused bicyclic lactone. This work vividly demonstrates that bioinspired skeletal reorganization is a useful strategy for simplifying the retrosynthetic analysis of structurally complex natural products.

Recent Developments with Icetexane Natural Products

Icetexane diterpenoids are a diverse family of natural products sourced from several species of terrestrial plants. Icetexanes exhibit a broad array of biological activities and together with their complex 6-7-6 tricyclic scaffolds, they have piqued the interest of synthetic organic chemists, natural products chemists, and biological investigators over the past four decades and were reviewed 13 years ago. This review summarizes icetexane natural products isolated since 2009, provides an overview of new synthetic approaches to the icetexane problem, and proposes an additional classification of icetexanes based on novel structures that are unlike previously isolated materials.

A Strategy toward Icetexane Natural Products

Icetexane diterpenoids are richly complex polycyclic natural products that have been described with a variety of biological activities. We report here a general synthetic approach toward the 6-7-6 tricyclic core structure of these interesting synthetic targets based on a two-step enolate alkylation and ring-closing metathesis reaction sequence.