Synthesis of macroheterocycles through intramolecular oxidative coupling of furanoid β-ketoesters

Palladium-catalyzed acetalization/cyclization of enynones with alcohols: rapid access to functionalized dihaloalkenyl dihydrofurans

A novel Pd-catalyzed acetalization/cyclization of enynones and alcohols for the construction of dihaloalkenyl dihydrofuran derivatives is described.

An Unexpected Transannular [4+2] Cycloaddition during the Total Synthesis of (+)-Norcembrene 5

We report a concise and versatile total synthesis of the diterpenoid (+)-norcembrene 5 from simple building blocks. Ring-closing metathesis and an auxiliary-directed 1,4-addition are the key steps of our synthetic route. During the synthesis, an unprecedented, highly oxidized pentacyclic structural motif was established from a furanocembranoid through transannular [4+2] cycloaddition.

Treasures old and new: what we can learn regarding the macrocyclic problem from past and present efforts in natural product total synthesis

In this review the strategies leading to successful macrocyclization, in the context of total synthesis are discussed.

Acylation Reactions of Dibenzo-7-phosphanorbornadiene: DFT Mechanistic Insights

Extensive DFT calculations provide deep mechanistic insights into the acylation reactions of tert-butyl dibenzo-7-phosphanobornadiene with PhCOX (X=Cl, Br, I, OTf) in CH2Cl2 solution. Such reactions are initialized by the nucleophilic P⋅⋅⋅C attack to the carbonyl group to form the acylphosphonium intermediate A+ together with X- anion, followed either by nucleophilic X-⋅⋅⋅P attack (X=Cl, Br, and I) toward A+ to eliminate anthracene or by slow rearrangement or decomposition of A+ (X=OTf). In contrast to the first case (X=Cl) that is rate-limited by the initial P⋅⋅⋅C attack, other reactions are rate-limited by the second X-⋅⋅⋅P attack for X=Br and I and even thermodynamically prevented for X=OTf, leading to isolable phosphonium salts. The rearrangement of phosphonium A+ is initiated by a P-C bond cleavage, followed either by sequential proton-shifts to form anthracenyl acylphosphonium or by deprotonation with additional base Et3N to form neutral anthracenyl acylphosphine. Our DFT results strongly support the separated acylphosphonium A+ as the key reaction intermediate that may be useful for the transfer of acylphosphenium in general.

Polycyclic Furanobutenolide-Derived Cembranoid and Norcembranoid Natural Products: Biosynthetic Connections and Synthetic Efforts

The polycyclic furanobutenolide-derived cembranoid and norcembranoid natural products are a family of congested, stereochemically complex, and extensively oxygenated polycyclic diterpenes and norditerpenes. Although the elegant architectures and biological activity profiles of these natural products have captured the attention of chemists since the isolation of the first members of the family in the 1990s, the de novo synthesis of only a single polycyclic furanobutenolide-derived cembranoid and norcembranoid has been accomplished. This article begins with a brief discussion of the proposed biosyntheses and biosynthetic connections among the polycyclic furanobutenolide-derived cembranoids and norcembranoids and then provides a comprehensive review of the synthetic efforts toward each member of the natural product family, including biomimetic, semisynthetic, and de novo synthetic strategies. This body of knowledge has been gathered to provide insight into the reactivity and constraints of these compact and highly oxygenated polycyclic structures, as well as to offer guidance for future synthetic endeavors.

Methods Utilizing First-Row Transition Metals in Natural Product Total Synthesis

First-row transition-metal-mediated reactions constitute an important and growing area of research due to the low cost, low toxicity, and exceptional synthetic versatility of these metals. Currently, there is considerable effort to replace existing precious-metal-catalyzed reactions with first-row analogs. More importantly, there are a plethora of unique transformations mediated by first-row metals, which have no classical second- or third-row counterpart. Herein, the application of first-row metal-mediated methods to the total synthesis of natural products is discussed. This Review is intended to highlight strategic uses of these metals to realize efficient syntheses and highlight the future potential of these reagents and catalysts in organic synthesis.

Radicals: Reactive Intermediates with Translational Potential

This Perspective illustrates the defining characteristics of free radical chemistry, beginning with its rich and storied history. Studies from our laboratory are discussed along with recent developments emanating from others in this burgeoning area. The practicality and chemoselectivity of radical reactions enable rapid access to molecules of relevance to drug discovery, agrochemistry, material science, and other disciplines. Thus, these reactive intermediates possess inherent translational potential, as they can be widely used to expedite scientific endeavors for the betterment of humankind.

Selective Pd-catalyzed α- and β-arylations of the furan rings of (ortho-bromophenyl)furan-2-yl-methanones: C(CO)–C bond cleavage with a furan ring as a leaving group and synthesis of furan-derived fluorenones

Selective palladium diacetate-catalyzed α- and β-arylations of the furan rings of (ortho-bromophenyl)furan-2-yl-methanones 1 under two different conditions are reported.

Palladium-catalyzed dearomatizing 2,5-alkoxyarylation of furan rings: diastereospecific access to spirooxindoles

A protocol for Pd-catalyzed intra- and intermolecular 2,5-alkoxyarylation reactions of furans to diastereospecifically synthesize two series of spirooxindoles is reported.

A strategy toward the synthesis of C13-oxidized cembrenolides

An efficient strategy for the construction of C₁₃-oxidized cembrenolides is reported. Central to this strategy is the installation of the C₁₃ hydroxyl group prior to cembrane macrocyclization (via formation of the C₁-C₂ bond), allowing access to both C₁₃ alcohol epimers. The orientation of the C₁₃ alcohol was found to influence the cyclization mode of the cembranolide scaffold upon furan oxidation, leading to motifs reminiscent to bipinnatolide F, bielschowskysin, and verrillin.