Successive Promotion of Formal [3+2] Cycloaddition of Aryl Methyl Ketones by I2 and Zn: Access to 2-Hydroxy-4-morpholin-2,5-diarylfuran-3(2H)-ones with a Quaternary Carbon Center.

2-Hydroxy-4-morpholin-2,5-diarylfuran-3(2H)-one derivatives were constructed sequentially using iodine and zinc dust from simple and readily available methyl ketone and morpholine as the starting materials. Under mild conditions, C-C, C-N, and C-O bonds formed in a one-pot synthesis. A quaternary carbon center was successfully constructed, and the active drug fragment morpholine was introduced into the molecule.

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.

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.

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.

One-Pot Synthesis of Diaryl 1,2-Diketones via Zn-Mediated Reductive Coupling.

A reductive coupling reaction was established for the synthesis of diaryl 1,2-dicarbonyl compounds from aryl methyl ketones in good yields. The mechanistic study showed the reaction undergoes C(CO)-C(sp3) bond cleavage, with the reductive coupling reaction occurring through an electron transfer process. Notably, the reaction not only is simple to operate but also has mild reaction conditions and a wide range of applicable substrates.

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.

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.

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.

Acid-Catalyzed Multicomponent Tandem Double Cyclization: A One-pot, Metal-free Route to Synthesize Polyfunctional 4,9-Dihydropyrrolo[2,1-b]quinazolines.

An acid-catalyzed multicomponent tandem double cyclization protocol has been developed for the synthesis of polyfunctional 4,9-dihydropyrrolo[2,1-b]quinazolines from simple and readily available arylglyoxal monohydrates, 2-aminobenzylamine, and trans-ß-nitrostyrenes. This practical and metal-free reaction proceeds through an imine formation/cyclization/Michael addition/Henry cyclization protocol, resulting in the construction of four new bonds and two ring moieties directly in one pot.

I2-Promoted gem-Diarylethene Involved Aza-Diels-Alder Reaction and Wagner-Meerwein Rearrangement: Construction of 2,3,4-Trisubstituted Pyrimido[1,2-b]indazole Skeletons.

A [3 + 1 + 2] cyclization-rearrangement reaction scheme was developed to synthesize pyrimido[1,2-b]indazoles from aryl methyl ketones, 3-aminoindazoles, and gem-diarylethenes. This metal-free process proceeds via a sequential aza-Diels-Alder reaction and Wagner-Meerwein rearrangement, and a possible reaction mechanism was demonstrated based on control experiments. This method exhibits good substrate compatibility and allows simple reaction conditions. Moreover, the products display significant aggregation-induced emission characteristics after simple modifications.

Direct Hydrodefluorination of CF3-Alkenes via a Mild SN2' Process Using Rongalite as a Masked Proton Reagent.

A concise and efficient hydrodefluorination process was developed for the synthesis of gem-difluoroalkenes. This reaction employs rongalite as a masked proton source and does not require any additional catalysts or reductants. Notably, trifluoromethyl alkenes having both terminal and internal double bonds are compatible with this process, allowing for a wider range of substrates. The successful late-stage functionalizations of pharmaceuticals and gram-scale syntheses were used to demonstrate the viability of this method.

Rongalite as C1 Synthon and Sulfone Source: A Practical Sulfonylmethylation Based on the Separate-Embedding Strategy.

Rongalite has been used in several challenging synthetic transformations with operationally simple and effective protocols. However, the employment of multiple characteristics of rongalite in synthetic chemistry is comparatively little known. Herein we report a separate-embedding type sulfonylmethylation of sulfoxonium ylides in which rongalite concurrently acted as a sulfone source, C1 synthon, radical initiator, and potential reducing reagent for the first time. Notably, this facile and easy-handling reaction does not require a catalyst or prefunctionalized sulfonylmethylation reagents.

I2-DMSO-Mediated N-H/α-C(sp3)-H Difunctionalization of Tetrahydroisoquinoline: Formal [2 + 2 + 1] Annulation for the Construction of Pyrrolo[2,1-a]isoquinoline Derivatives.

An I2-DMSO-mediated cascade reaction using methyl ketones and 1,2,3,4-tetrahydroisoquinolines (THIQs) as commercially available substrates has been developed for the construction of pyrrolo[2,1-a]isoquinoline derivatives. This metal-free process involves N-H/α-C(sp3)-H difunctionalization of THIQ. Two C-C bonds and one C-N bond are formed in one pot under mild conditions. Besides, a quaternary carbon center has been constructed in this transformation efficiently.

I2-DMSO Mediated Multicomponent [3+2] Annulation Reaction: An Approach to Pyrrolo[2,1-a]isoquinoline Derivatives with a Quaternary Center.

An I2-DMSO mediated multicomponent [3+2] cascade annulation reaction using methyl ketones, 1,2,3,4-tetrahydroisoquinolines (THIQ) and cyclopropenones as readily available substrates has been developed. This metal-free process involves N-H/α-C(sp3)-H trifunctionalization of THIQ and C-C bond cleavage of cyclopropenone, providing a direct approach to obtain pyrrolo[2,1-a]isoquinoline derivatives with a quaternary carbon center. Two C-C bonds and one C-N bond are formed efficiently in one pot.

Synthesis of Tetrahydro-2H-thiopyran 1,1-Dioxides via [1+1+1+1+1+1] Annulation: An Unconventional Usage of a Tethered C-S Synthon.

An unprecedented [1+1+1+1+1+1] annulation process has been developed for the construction of tetrahydro-2H-thiopyran 1,1-dioxides. Notably, rongalite acted as a tethered C-S synthon in this reaction and can be chemoselectively used as triple C1 units and as a source of sulfone. Mechanistic investigation indicated that two different carbon-increasing models are involved in this reaction in which rongalite serves as C1 units.

Palladium catalyzed annulation of 2-iodobiphenyl with a non-terminal alkene enabled by neighboring group assistance.

In this work, an efficient palladium catalyzed annulation of 2-iodobiphenyl with a non-terminal alkene was developed. The key factor in this transformation was the formation of a highly reactive oxo-palladacycle intermediate, which was enabled by a neighboring hydroxyl group, and remarkably restrained the ß-H elimination process. Mechanistically, control experiments demonstrated that the hydroxyl group may act as an anionic ligand, which was irreplaceable in this reaction. This transformation presented good reactivity and selectivity, and no simple Heck coupling products were detected for all of the explored substrates.

Access to 2-arylquinazolines via catabolism/reconstruction of amino acids with the insertion of dimethyl sulfoxide.

Quinazoline skeletons are synthesized by amino acid catabolism/reconstruction combined with the insertion/cyclization of dimethyl sulfoxide for the first time. The amino acid acts as a carbon and nitrogen source through HI-mediated catabolism and is then reconstructed using aromatic amines and dimethyl sulfoxide (DMSO) as a one-carbon synthon. This protocol is of great significance for the further study of the conversion of amino acids.

Rongalite as a sulfone source: a novel copper-catalyzed sulfur dioxide anion incorporation process.

A novel copper-catalyzed sulfur dioxide anion incorporation cascade for the synthesis of 1-thiaflavanone sulfones has been disclosed using rongalite as an economic and safe sulfone source. A series of 1-thiaflavanone sulfones were synthesized from easily prepared 2'-iodochalcone derivatives in excellent yields. This transformation proceeds through consecutive formation of two C-S bonds, which is the first example of SO- being used to construct sulfone motifs under copper-catalyzed conditions.

Quadruple C-H activation coupled to hydrofunctionalization and C-H silylation/borylation enabled by weakly coordinated palladium catalyst.

Unlike the well-reported 1,2-difunctionalization of alkenes that is directed by classic pyridine and imine-containing directing groups, oxo-palladacycle intermediates featuring weak Pd-O coordination have been less demonstrated in C-H activated cascade transformations. Here we report a quadruple C-H activation cascade as well as hydro-functionalization, C-H silylation/borylation sequence based on weakly coordinated palladium catalyst. The hydroxyl group modulates the intrinsic direction of the Heck reaction, and then acts as an interrupter that biases the reaction away from the classic ß-H elimination and toward C-H functionalization. Mechanistically, density functional theory calculation provides important insights into the key six-membered oxo-palladacycle intermediates, and indicates that the ß-H elimination is unfavorable both thermodynamically and kinetically. In this article, we focus on the versatility of this approach, which is a strategic expansion of the Heck reaction.