An I2-DMSO catalytic manifold enabled aromatization for C-ring editing of podophyllotoxone.

The precise aromatization of the C-ring of podophyllotoxone to access value-added dehydropodophyllotoxin derivatives conventionally requires the use of equivalent amounts of unsustainable oxidants and suffers from inefficiencies. Taking advantage of the hydridic character of the C8 and C8' of podophyllotoxone, we have developed an I2-DMSO catalytic manifold that enables a green and selective dehydrogenative aromatization to overcome these synthetic challenges. An unprecedented dehydrogenative amination of podophyllotoxone derivatives was also realized using aniline as the reaction partner.

Aniline assisted dimerization of phenylalanines: convenient synthesis of 2-aroyl-3-arylquinoline in an I2-DMSO system.

We herein report an efficient synthesis of 2-aroyl-3-arylquinolines from phenylalanines and anilines. The mechanism involves I2-mediated Strecker degradation enabled catabolism and reconstruction of amino acids and a cascade aniline-assisted annulation. Both DMSO and water act as oxygen sources in this convenient protocol.

A Pummerer Reaction-Enabled Modular Synthesis of Alkyl Quinoline-3-carboxylates and 3-Arylquinolines from Amino Acids.

Concise synthesis of functionalized quinolines has received continuous research attention owing to the biological importance and synthetic potential of bicyclic N-heterocycles. However, synthetic routes to the 2,4-unsubstituted alkyl quinoline-3-carboxylate scaffold, which is an important motif in drug design, remain surprisingly limited, with modular protocols that proceed from readily available materials being even more so. We herein report an acidic I2-DMSO system that converts readily available aspartates and anilines into alkyl quinoline-3-carboxylate. This method can be extended to a straightforward synthesis of 3-arylquinolines by simply replacing the aspartates with phenylalanines. Mechanistic studies revealed that DMSO was activated by HI via a Pummerer reaction to provide the C1 synthon, while the amino acid catabolized to the C2 synthon through I2-mediated Strecker degradation. A formal [3 + 2 + 1] annulation of these two concurrently generated synthons with aniline was responsible for the selective formation of the quinoline core. The synthetic utility of this protocol was illustrated by the efficient synthesis of human 5-HT4 receptor ligand. Moreover, an unprecedented chemoselective synthesis of 2-deuterated, 3-substituted quinoline, featuring this reaction, has been established.

Switching Over of the Chemoselectivity: I2-DMSO-Enabled α,α-Dichlorination of Functionalized Methyl Ketones.

Precise control of the chemoselectivity of the halogenation of a substrate equipped with multiple nucleophilic sites is highly demanding and challenging. Most reported chlorinations of methyl ketones show poor compatibility or even exclusive selectivity toward electron-rich arene, olefin, and alkyne residues. This is attributed to the direct or in situ employment of electrophilic Cl2/Cl+ species. Here, we reported that, even bearing those competitive residues, methyl ketones can still undergo dichlorination to afford α,α-dichloroketones in a chemo-specific manner. Enabled by the I2-dimethyl sulfoxide catalytic system, in which hydrochloric acid only acts as a nucleophilic Cl- donor, this straightforward dichlorination reaction is safe and operator-friendly and has high atomic economy, giving access to structurally diverse α,α-dichloroketones in good yields and with good functional-group tolerance.

Taming the radical cation intermediate enabled one-step access to structurally diverse lignans.

Lignans, in spite of their structural diversity, are all biosynthetically derived from coniferyl alcohol. We report herein a divergent synthesis of lignans from biomass-derived monolignols in a short synthetic sequence. Blue LED irradiation of a dichloromethane solution of dicinnamyl ether derivatives in the presence of Cu(TFA)2, an alcohol (2.0 equiv) and a catalytic amount of Fukuzumi's salt affords the C7-alkoxylated aryltetralin cyclic ethers. Increasing the amount of alcohol under otherwise identical conditions diverts the reaction course to furnish the C7,C7'-dialkoxylated dibenzyltetrahydrofurans, while replacing Cu(TFA)2 with diphenyl disulfide (PhSSPh) provides selectively the C7-monoalkoxylated dibenzyltetrahydrofurans. Aza-, thia- and carba-analogues of lignans are equally accessible by simply changing the tethering atom of the allylic alcohols. Concise total syntheses of aglacins A, E, F, brassilignan, and dehydrodimethylconidendrin are documented featuring these transformations.

Radical-Cation Cascade to Aryltetralin Cyclic Ether Lignans Under Visible-Light Photoredox Catalysis.

The development of concise, sustainable, and cost-effective synthesis of aryltetralin lignans, bearing either a fused lactone or cyclic ether, is of significant medicinal importance. Reported is that in the presence of Fukuzumi's acridinium salt under blue LED irradiation, functionalized dicinnamyl ether derivatives are converted into aryltetralin cyclic ether lignans with concurrent generation of three stereocenters in good to high yields with up to 20:1 diastereoselectivity. Oxidation of an alkene to the radical cation is key to the success of this formal Diels-Alder reaction of electronically mismatched diene and dienophile. Applying this methodology, six natural products, aglacin B, aglacin C, sulabiroin A, sulabiroin B, gaultherin C, and isoshonanin, are synthesized in only two to three steps from readily available biomass-derived monolignols. A revised structure is proposed for gaultherin C.

Aryldiazonium Salts Serve as a Dual Synthon: Construction of Fully Substituted Pyrazoles via Rongalite-Mediated Three-Component Radical Annulation Reaction.

A highly efficient rongalite-mediated three-component radical annulation reaction to furnish fully substituted pyrazoles from aryldiazonium salts and α,ß-unsaturated aldehydes or ketones under metal- and oxidant-free conditions at room temperature has been developed. In this transformation, aryldiazonium salts served as the precursor of both the aryl and aryl hydrazine units. Mechanistic investigations indicated that rongalite could act as a radical initiator and reducing reagent simultaneously in the reaction.

Palladium-Catalyzed C-H Diarylation of Ferrocenecarboxylic Acids with Aryl Iodides.

Palladium-catalyzed C-H diarylation of ferrocenes is described. In the presence of 10 mol % Pd(OAc)2, direct C-H diarylation reactions of commercially available ferrocenecarboxylic acid with aryl iodides proceeded smoothly to afford diarylated ferrocenes bearing a variety of functional groups in moderate to good yields. The carboxylic group could also act as a remote directing group to result in the third arylation on the other Cp ring of ferrocene.

I2/DMSO-mediated multicomponent reaction of o-hydroxyaryl methyl ketones, rongalite, and DMSO: access to C3-sulfenylated chromones.

An efficient I2-DMSO reagent system-mediated multicomponent reaction strategy for the synthesis of C3-sulfenylated chromones from o-hydroxyaryl methyl ketones, rongalite, and dimethyl sulfoxide has been developed. Notably, the double C-S bond cleavages of rongalite and dimethyl sulfoxide served as key steps in this smooth transformation, affording the C1 unit and sulfur source for the assembly of C3-sulfenylated chromones. Preliminary mechanistic studies indicated that in situ generated HCHO and (2-(2-hydroxyphenyl)-2-oxoethyl)dimethylsulfonium iodine were probably the key intermediates in this transformation.

One-Pot Total Synthesis of Evodiamine and Its Analogues through a Continuous Biscyclization Reaction.

The one-pot total synthesis of evodiamine and its analogues is achieved using a three-component reaction. Through continuous biscyclization, various readily available substrates with good functional group tolerance were easily incorporated into biologically active quinazolinocarboline backbones. The use of triethoxymethane as a cosolvent was crucial for this quick and straightforward transformation.

Direct Biomimetic Synthesis of ß-Carboline Alkaloids from Two Amino Acids.

The increasing importance of enzyme mimics in organic synthesis inspired us to design a novel biomimetic synthesis of ß-carboline alkaloids directly from tryptophan and a second amino acid. This novel one-pot protocol utilizes abundant and readily available starting materials and thus presents a green and user-friendly alternative to conventional methods that rely on stepwise synthesis. Driven by molecular iodine and TFA, decarboxylation, deamination, Pictet-Spengler reaction, and oxidation reactions proceeded sequentially, transforming biomass amino acids into value-added alkaloid motifs.

The triple role of rongalite in aminosulfonylation of aryldiazonium tetrafluoroborates: synthesis of N-aminosulfonamides via a radical coupling reaction.

A simple and convenient method for N-aminosulfonamide synthesis from the cross-coupling of aryldiazonium tetrafluoroborates and rongalite under metal-free, oxidant-free, and room-temperature conditions is reported. This method does not require an external amine source, with the aryldiazonium tetrafluoroborates participating as both an aryl radical and a potential amine source in the transformation. Mechanistic studies revealed that rongalite could act as a radical initiator, a sulfur dioxide surrogate and a reducing reagent simultaneously in this reaction.

C(sp3)-H Bond Functionalization of Benzo[ c]oxepines via C-O bond Cleavage: Formal [3+3] Synthesis of Multisubstituted Chromans.

An efficient base-promoted C(sp3)-H bond functionalization strategy for the synthesis of multisubstituted chromans from the formal [3+3] cycloaddition of benzo[ c]oxepines and electron-rich phenols has been developed. The corresponding 4 H-chromenes can be easily obtained in excellent yields by simple filtration from chromans. Preliminary mechanistic studies indicate that the C-O bond cleavage is the key step for the C(sp3)-H bond functionalization and that this reaction could have occurred through tandem C-O bond cleavage/Michael addition/annulation reactions.

A C-H Oxidation/Two-Fold Cyclization Approach to Imidazopyridoindole Scaffold under Mild Oxidizing Conditions.

An expeditious one-step synthesis of the imidazopyridoindole scaffold was achieved through the C-H oxidation/two-fold cyclization reaction of methyl ketone and tryptamine derivatives. Mild oxidizing conditions were employed to realize the efficient oxidation of C(sp3)-H bonds, while suppressing overoxidation of the intermediate and ensuring the cross-trapping of two in situ generated acylimine intermediates.

Divergent Synthesis of Functionalized Quinolines from Aniline and Two Distinct Amino Acids.

A practicable quinoline synthesis from aniline and two amino acids was developed for generating a wide range of quinolines with high efficiency and diversity. Thus, it facilitated the creations of pharmaceutical derivatives, photochemical active compounds, and challenging scaffolds. The concept of using two amino acids as heterocyclic precursors has been raised for the first time. Mechanistic studies revealed that I2 enabled decarboxylation, oxidative deamination, and selective reconstruction of new C-N and C-C bonds processes.

Oxidative Trimerization of Amino Acids: Selective Synthesis of 2,3,5-Trisubstituted Pyridines.

An oxidative trimerization of three amino acids has been realized to furnish 2,3,5-trisubstuitued pyridines in both cross- and homo-trimerization types. This method is capable of converting simple linear biomass material to heterocycles, which features in the assembly of three amino acid branched chains into one aromatic ring. Molecular iodine triggers the sequential decarboxylation and deamination of amino acids and then promotes the selective formation of new C-N and C-C bonds.

Direct Construction of 4-Hydroxybenzils via Para-Selective C-C Bond Coupling of Phenols and Aryl Methyl Ketones.

A highly para-selective C-C bond coupling is presented between phenols C(sp(2)) and aryl methyl ketones C(sp(3)), which enables the direct construction of 4-hydroxybenzil derivatives. This practical method exhibits a broad substrate scope and large-scale applicability and represents a general gateway to the hydroxybenzil natural product family. Mechanistic investigations indicated that the combination of HI with DMSO realized the oxidative carbonylation of aryl methyl ketones, while boric acid acted as a dual-functional relay reagent to promote this transformation.

Synthesis of 2,4,5-Trisubstituted Furans via a Triple C(sp(3))-H Functionalization Reaction Using Rongalite as the C1 Unit.

A highly efficient I2/Cu(NO3)2·3H2O-mediated triple C(sp(3))-H functionalization reaction for the synthesis of 2,4,5-trisubstituted furans from aryl methyl ketones and rongalite by employing rongalite as a C1 unit has been developed. This method allows rapid access to (2-acyl-4-methylthio-5-aryl) furans. Preliminary mechanistic studies indicate that in situ generated dimethyl(phenacyl)-sulfonium iodine and HCHO were probably the key intermediates in this transformation.

Molecular Iodine-Mediated Chemoselective Synthesis of Multisubstituted Pyridines through Catabolism and Reconstruction Behavior of Natural Amino Acids.

A new process has been developed for the selective construction of 2,6-disubstituted, 2,4,6-trisubstituted, and 3,5-disubstituted pyridines based on the catabolism and reconstruction behaviors of amino acids. Molecular iodine was used as a tandem catalyst to trigger the decarboxylation-deamination of amino acids and to promote the subsequent formation of the pyridine products.

Direct synthesis of substituted naphthalenes from 1,3-dicarbonyl compounds and 1,2-bis(halomethyl)benzenes including a novel rearrangement aromatization of benzo[c]oxepine.

An unexpected rearrangement aromatization of benzo[c]oxepine has been revealed to synthesize substituted naphthalenes. This observation was further exploited to develop an efficient approach for the construction of naphthalenes from simple and commercially available 1,3-dicarbonyl compounds and 1,2-bis(halomethyl)benzene compounds via a new domino reaction sequence.