Synthesis of the entire framework of tartrolon B utilizing a silicon-tethered ring-closing metathesis strategy

Recent Advances in One-Pot Enyne Metathesis Processes for the Preparation of Biologically and Medicinally Relevant Compounds

Enyne metathesis reactions are powerful tools for the preparation of a wide range of synthetic and natural chemical substances with increasing efficiency and environmental sustainability. The driving force of the reaction is the formation of a stable conjugated system, i.e., a diene, which through further functionalization steps can be used for the construction of skeletally complex molecular architectures. These concepts are exploited to design cascade reaction sequences, where multiple rings can be formed in a one-pot fashion by combining metathetic protocols with various chemical transformations. The strong correlation between synthetic organic chemistry and medicinal chemistry prompted us to review the most notable approaches for the synthesis of biologically relevant compounds via enyne metathesis-based one-pot processes. With the aim to provide a modern and practical overview, by taking into consideration the scientific literature on this topic, we have focused the majority of our attention on the research performed in the last decade. This review covers the literature from 2003 to 2020.

1 Introduction

2 Ethylene-Mediated Processes

3 RCEYM/CM and CEYM/RCM Processes

4 Enyne Metathesis/Diels–Alder-Based Processes

5 RCM of Dienynes

6 RCM of Tethered Dienynes

7 Relay Metathesis

8 Ring-Rearrangement Metathesis

9 RCEYM/Transition-Metal-Catalyzed C–C Bond-Forming Processes

10 Conclusions

11 List of Acronyms

Synthesis of cyclic alkenylsiloxanes by semihydrogenation: a stereospecific route to (Z)-alkenyl polyenes

Cyclic alkenylsiloxanes were synthesized by semihydrogenation of alkynylsilanes-a reaction previously plagued by poor stereoselectivity. The silanes, which can be synthesized on multigram scale, undergo Hiyama-Denmark coupling to give (Z)-alkenyl polyene motifs found in bioactive natural products. The ring size of the silane is crucial: five-membered cyclic siloxanes also couple under fluoride-free conditions, whilst their six-membered homologues do not, enabling orthogonality within this structural motif.

Tartrolon D, a cytotoxic macrodiolide from the marine-derived actinomycete Streptomyces sp. MDG-04-17-069

Exploration of marine-derived actinomycetes as a source of antitumor compounds has led to the isolation of a new member of the tartrolon series, tartrolon D (4). This new compound was obtained from Streptomyces sp. MDG-04-17-069 fermentation broths and displayed strong cytotoxic activity against three human tumor cell lines. Additionally, the known compound ikarugamycin (5) was also found in the culture broths of the same microorganism. The structure of this new tartrolon was established by a combination of spectroscopic techniques (1D and 2D NMR, HRMS, and UV) as well as by comparison with published data for similar compounds.

Application of tandem ring-closing enyne metathesis: formal total synthesis of (-)-cochleamycin A

A tandem ring-closing metathesis of a silaketal-based dienyne substrate proceeded efficiently to provide a bicyclic siloxane, which upon removal of the silicon tether afforded an (E,Z)-1,3-dienediol. Further manipulation of this key functional motif rendered synthesis of the entire C1-C19 linear skeleton of (-)-cochleamycin A, a late-stage intermediate employed in the previous total synthesis of (+)-cochleamycin A by Roush and co-workers.