Eight‐Step Total Synthesis of Phalarine by Bioinspired Oxidative Coupling of Indole and Phenol

Solar-Light-Driven Photocatalytic Oxidative Coupling of Phenol Derivatives over Bismuth-Based Porous Metal Halide Perovskites

The selective oxidative coupling of phenol derivatives, involving carbon-carbon (C-C) and carbon-oxygen (C-O) bond formation, has emerged as a critical approach in the synthesis of natural products. However, achieving precise control over the selectivity in coupling reactions of unsubstituted phenols utilizing solar light as the driving force remains a big challenge. In this study, we report a series of porous Cs3Bi2X9 (X=Cl, Br, I) photocatalysts with tailored band gaps and compositions engineered for efficient solar-light-driven oxidative phenol coupling. Notably, p-Cs3Bi2Br9 exhibited about 73 % selectivity for C-C coupling, displaying a high formation rate of 47.3 μmol gcat -1 h-1 under solar radiation. Furthermore, this approach enables control of the site-selectivity for phenol derivatives on Cs3Bi2X9, enhancing C-C coupling. The distinctive porous structure and appropriate band-edge positions of Cs3Bi2Br9 facilitated efficient charge separation, and surface interaction/activation of phenolic hydroxyl groups, resulting in the kinetically preferred formation of C-C over C-O bond. Mechanistic insights into the reaction pathway, supported by comprehensive control experiments, unveiled the crucial role of interfacial charge transfers and Lewis acid Bi sites in stabilizing phenolic intermediates, thereby directing the regioselectivity of diradical couplings and resulting in the formation of unsymmetrical biphenols.

Bioinspired Total Synthesis of Bipolarolides A and B

We have achieved the first total synthesis of bipolarolides A and B, which possess an intriguing and complex 5/6/6/6/5 caged pentacyclic skeleton with seven contiguous stereocenters. The synthesis features a lithium-halogen exchange/intermolecular nucleophilic addition to link two enantioenriched fragments, two ring-closing metathesis reactions to assemble the five- and eight-membered rings, and a bioinspired Prins reaction/ether formation cascade cyclization to construct the 5/6/6/6/5 caged skeleton.

Synthesis of Indoles Using the Electrophilic Potential of Diazirines

The electrophilic potential of diazirines has been utilized to obtain N-substituted diaziridines that are directly hydrolyzed to produce monosubstituted hydrazines. The hydrazines can undergo the Fisher process with enolizable carbonyls to yield multiple indole derivatives in moderate to high yields. The N-metalated diaziridine intermediates can undergo isomerization prior to electrophilic substitution, to form N,N-disubstituted hydrazones. The latter react with enolizable carbonyls to produce N-protected indole derivatives in a single step. This protocol was used to efficiently synthesize indomethacin, an anti-inflammatory drug.

Total Synthesis of (+)-Aberrarone

The structurally intriguing diterpene (+)-aberrarone has been assembled in only 12 steps from the commercially available (S,S)-carveol without protecting group manipulations. This concise synthesis features a Cu-catalyzed asymmetric hydroboration to generate the chiral methyl group, a Ni-catalyzed reductive coupling to link two fragments, and a Mn-mediated radical cascade cyclization to construct the triquinane system.

Unraveling the Structure and Reactivity Patterns of the Indole Radical Cation in Regioselective Electrochemical Oxidative Annulations

Oxidation-induced strategy for inert chemical bond activation through highly active radical cation intermediate has exhibited unique reactivity. Understanding the structure and reactivity patterns of radical cation intermediates is crucial in the mechanistic study and will be beneficial for developing new reactions. In this work, the structure and properties of indole radical cations have been revealed using time-resolved transient absorption spectroscopy, in situ electrochemical UV-vis, and in situ electrochemical electron paramagnetic resonance (EPR) technique. Density functional theory (DFT) calculations were used to explain and predict the regioselectivity of several electrochemical oxidative indole annulations. Based on the understanding of the inherent properties of several indole radical cations, two different regioselective annulations of indoles have been successfully developed under electrochemical oxidation conditions. Varieties of furo[2,3-b]indolines and furo[3,2-b]indolines were synthesized in good yields with high regioselectivities. Our mechanistic insights into indole radical cations will promote the further development of oxidation-induced indole functionalizations.

Synthesis of 3-Acyloxyindolenines by TiCl3-Mediated Reductive Cyclization of 2-(ortho-Nitroaryl)-Substituted Enol Esters

In the presence of TiCl₃, the reductive cyclization of tetrasubstituted enol esters bearing a 2-(ortho-nitroaryl) substituent affords 3-acyloxy-2,3-disubstituted indolenines in good yields. A domino process involving the partial reduction of nitro to a nitroso group followed by 5-center-6π-electrocyclization, 1,2-acyloxy migration, and the further reduction of the resulting nitrone intermediate accounts for the reaction outcome. The so-obtained indolenines are converted smoothly to 2,2-disubstituted oxindoles via a sequence of saponification and semipinacol rearrangement.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Divergent Total Synthesis of Four Kopsane Alkaloids: N-Carbomethoxy-10,22-dioxokopsane, Epikopsanol-10-lactam, 10,22-Dioxokopsane, and N-Methylkopsanone

We have achieved the divergent total synthesis of four kopsane alkaloids which share a complex heptacyclic caged ring system. Key transformations include an asymmetric Diels-Alder reaction to assemble the central bicyclo[2.2.2]octane moiety and the quaternary stereocenter at C20, a SmI₂ -mediated cascade reduction/aldol reaction to construct the five-membered ring and the quaternary stereocenter at C7, and a late-stage cascade reductive amination/cyclization to establish the highly strained caged ring system.

Bioinspired Total Synthesis of (+)-Euphorikanin A

We have achieved a bioinspired total synthesis of (+)-euphorikanin A, which possesses an intriguing and complex 5/6/7/3-fused tetracyclic skeleton bearing a bridged [3.2.1]-γ-lactone moiety. Key transformations include stereoselective alkylation and aldol condensation to install the main stereocenters, an intramolecular nucleophile-catalyzed aldol lactonization of carboxylic acid-ketone to assemble the five-membered ring, a McMurry coupling to construct the seven-membered ring, and a biomimetic benzilic acid type rearrangement to form the bridged [3.2.1]-γ-lactone moiety.

Regio- and Stereoselective Cascade of β,γ-Unsaturated Ketones by Dipeptided Phosphonium Salt Catalysis: Stereospecific Construction of Dihydrofuro-Fused [2,3-b] Skeletons

Chiral (dihydro)furo-fused heterocycles are significant structural motifs in numerous natural products, functional materials and pharmaceuticals. Therefore, developing efficient methods for preparing compounds with these privileged scaffolds is an important endeavor in synthetic chemistry. Herein, we develop an effective, modular method by a dipeptide-phosphonium salt-catalyzed regio- and stereoselective cascade reaction of readily available linear β,γ-unsaturated ketones with aromatic alkenes, affording a wide variety of structurally fused heterocyclic molecules in high yields with excellent stereoselectivities. Moreover, mechanistic investigations revealed that the bifunctional phosphonium salt controlled the regio- and stereoselectivities of this cascade reaction, particularly proceeding through the initial ketone α-addition followed by O-participated substitution; and the multiple hydrogen-bonding interactions between Brønsted acid moieties of catalyst and nitro group of aromatic alkene were crucial in asymmetric induction. Given the generality, versatility, and high efficiency of this method, we anticipate that it will have broad synthetic utilities.

Recent Advances and the Prospect of Hypervalent Iodine Chemistry

Nowadays, hypervalent iodine chemistry has remarkably advanced in parallel with the emergence of novel hypervalent iodine reagents. Hypervalent iodine reagents, due to their outstanding characteristics including rich reactivities, excellent chemoselectivity, stability, and environmental friendliness, are becoming more and more popular in the synthetic organic chemistry. In this Account, a number of recent elegant research works and our perspective on the future of hypervalent iodine chemistry is presented.

1 Introduction

2 Recent Advances and Discussion

2.1 Novel Reactivities of Hypervalent Iodine Reagents

2.2 Atom-Economical Reactions Promoted by Hypervalent Iodine Reagents

2.3 Other Applications of Hypervalent Iodine Reagents

2.4 The Applications of DFT Calculations in Elucidating Reaction Mechanism Involving Hypervalent Iodine Reagents

3 Outlook and Conclusion

Natural Products Originated from the Oxidative Coupling of Tyrosine and Tryptophan: Biosynthesis and Bioinspired Synthesis

The oxidative coupling of tyrosine and tryptophan units is a pivotal step in the total synthesis of some peptide-derived marine and terrestrial natural products, such as the diazonamides, azonazine and tryptorubin A. This Minireview details the biosynthesis and bioinspired synthesis of natural products with such structures. A special focus is put on the challenges of the synthesis of these natural products and the innovative solutions adopted by synthetic chemists.

Innovation of hypervalent(iii) iodine in the synthesis of natural products

The focus article discusses the innovation of hypervalent(iii) iodine regarding skeletal rearrangement, cycloaddition and cyclization, and sp³ C–H functionalization in natural product synthesis.

Dearomatization Reactions of Indoles to Access 3D Indoline Structures

This Account summarizes our involvement in the development of dearomatization reactions of indoles that has for origin a total synthesis problematic. We present the effort from our group to obtain 3D-indolines scaffold from the umpolung of N-acyl indoles via activation with FeCl3 to the oxidative spirocyclizations of N-EWG indoles and via the use of electrochemistry.

1 Introduction

2 Activation of N-Acyl Indoles with FeCl3

2.1 Hydroarylation of N-Acyl Indoles

2.2 Difunctionalization of N-Acyl Indoles

3 Radical-Mediated Dearomatization of Indoles for the Synthesis of Spirocyclic Indolines

4 Electrochemical Dearomatization of Indoles

4.1 Direct Electrochemical Oxidation of Indoles

4.2 Indirect Electrochemical Oxidation of Indoles

5 Conclusion

Diastereoselective construction of the benzannulated spiroketal core of chaetoquadrins enabled by a regiodivergent cascade

A remarkable acid-mediated methodology for the regiodivergent construction of a biologically interesting tricyclic benzannulated-spiroketal skeleton with diastereomeric specificity was uncovered to efficiently access analogs of chaetoquadrins .

Construction of Bisindolines via Oxidative Coupling Cyclization

Herein, we report a general approach for the efficient construction of three-dimensional bisindolines via oxidative coupling cyclization in an intermolecular manner. This reaction is featured by its operational simplicity, metal-free conditions, lack of protecting group, and high selectivity. Notably, a wide range of anilines are suitable in this intermolecular cyclization, furnishing corresponding bisindolines in up to 98% yield.