Oxidative Tandem Cyclization of Glycine Esters with Propargyl Alcohols.

A facile and efficient aerobic oxidative (4 + 2)-cyclization/aromatization/lactonization tandem reaction of N-aryl glycine esters with propargyl alcohols to access quinoline-fused lactones is reported. The reaction can be extended to homopropargylic alcohols too. The transformation is straightforward to perform under mild conditions and scalable, and both reaction components are readily available.

Recent progress in organophotoredox reaction.

In the past decade, visible light photoredox catalysis has been established as a gentle and powerful strategy for the activation of organic molecules. As an important part of this, organic photocatalysts are widely used in chemical synthesis due to their attributes, such as cheapness and relatively high redox potential. In this article, we review the related organic reactions promoted by visible light in the presence of various organic photocatalysts over the past 5 years. The reaction mechanisms involving single electron transfer, energy transfer and proton-coupled electron transfer are also discussed. The recovery and reuse of some supported organic photocatalysts are highlighted. Moreover, prospects for the development of organic photocatalysts are emphasized.

Synthesis of 10H-indolo[1,2-a]indol-10-ones via palladium-catalyzed C-H bond activation and difluorocarbene transfer.

A Pd-catalyzed annulation between 1-(2-iodophenyl)-1H-indoles and sodium difluorochloroacetate has been developed to synthesize 10H-indolo[1,2-a]indol-10-one derivatives via C-H bond activation and difluorocarbene transfer. Our route enables facile access to the targeted products with various substituents in moderate to high yields. This method features high reactivity, good functional group tolerance, a simple operation procedure, and mild reaction conditions. The reaction can be carried out on a gram scale.

Visible-Light-Promoted Diboron-Mediated Transfer Hydrogenation of Azobenzenes to Hydrazobenzenes.

A visible-light-promoted transfer hydrogenation of azobenzenes has been developed. In the presence of B2pin2 and upon visible-light irradiation, the reactions proceeded smoothly in methanol at ambient temperature. The azobenzenes with diverse functional groups have been reduced to the corresponding hydrazobenzenes with a yield of up to 96%. Preliminary mechanistic studies indicated that the hydrogen atom comes from the solvent and the transformation is achieved through a radical pathway.

Visible-light-promoted selective O-alkylation of 2-pyridones with α-aryldiazoacetates.

A visible-light-promoted O-H insertion reaction between 2-pyridones and α-aryldiazoacetates has been developed. Upon visible light irradiation, the reaction proceeds smoothly under mild and catalyst-free conditions. A wide scope of 2-pyridones and α-aryldiazoacetates are well tolerated, and various O-alkylated 2-pyridones are obtained with perfect selectivity and good functional group tolerance. A photoinduced radical process is probably responsible for the excellent selectivity.

Catalyst-free, visible-light-promoted S-H insertion reaction between thiols and α-diazoesters.

A visible-light-promoted S-H insertion reaction between thiols and α-diazoesters was developed. The reaction proceeded smoothly at room temperature with a broad substrate scope, affording various thioethers in moderate to excellent yields. The catalyst- and additive-free nature, sustainable energy source and mild reaction conditions make this strategy more eco-friendly.

Visible-light-promoted acyl radical cascade reaction for accessing acylated isoquinoline-1,3(2H,4H)-dione derivatives.

A visible-light-promoted decarboxylative acyl radical acylation/cyclization cascade reaction of N-methacryloylbenzamides for accessing acylated isoquinoline-1,3(2H,4H)-dione derivatives was described. In this report, α-keto acids were used for generating acyl radicals and inducing radical acylations. This protocol features mild reaction conditions, operational practicality and a broad substrate scope.

Diastereoselective synthesis of spiro-cyclopropanyl-cyclohexadienones via direct sulfide-catalyzed [2 + 1] annulation of para-quinone methides with bromides.

An efficient sulfide-catalyzed [2 + 1] annulation of para-quinone methides (p-QMs) with diverse bromides has been achieved. This catalytic strategy provides an efficient and straightforward protocol for accessing a variety of spiro-cyclopropanyl-cyclohexadienone compounds in good to excellent yields (64% to 96% yields) with outstanding diastereoselectivities (>20 : 1 dr), displaying good functional group tolerance as well as gram-scale capacity.

Double-Oxidative Dehydrogenative [4+2]-Cyclization/Dehydrogenation/Oxygenation Tandem Reaction of N-Arylglycine Derivatives with Cumenes.

Double-oxidative dehydrogenative (DOD) cyclization is one of the most straightforward strategies for the synthesis of cyclic compounds. A novel approach to substituted 3,4-dihydroquinoline-3-one derivatives via a Cu(II)/DDQ/O2 system-catalyzed DOD [4+2]-cyclization/dehydrogenation/oxygenation cascade reaction of N-arylglycine derivatives, cumenes, and O2 has been developed.

[3 + 2] Cycloaddition of para-Quinone Methides with Nitrile Imines: Approach to Spiro-pyrazoline-cyclohexadienones.

[3 + 2] cycloaddition of para-quinone methides with nitrile imines under mild conditions has been achieved. The corresponding spiro-pyrazoline-cyclohexadienone products were constructed in good to excellent yields (up to 97% yield) with high regioselectivity. This straightforward protocol exhibits good functional group tolerance and scalability and provides the spiro-pyrazoline-cyclohexadienones.

Double C-N bond cleavages of N-alkyl 4-oxopiperidinium salts: access to unsymmetrical tertiary sulfonamides.

In this paper, regiospecific, double intraannular C-N bond cleavages of N-alkyl 4-oxopiperidinium salts are presented. The reaction sequence involves a charge-transfer complex, in situ formed between sulfonyl chloride and N-methylmorpholine, which induces S-Cl bond homolysis of sulfonyl chloride, yielding a reactive sulfonyl radical that further induces the double C-N bond cleavages of N-alkyl 4-oxopiperidinium salt. The secondary amine thus produced was trapped by sulfonyl chloride to yield the desired sulfonamide product. The key feature of this protocol is that two intraannular C-N bonds of the 4-oxopiperidine ring are cleaved in one step under metal- and oxidant-free conditions.

Tandem radical cyclization of N-methacryloyl benzamides with CBr4 to construct brominated isoquinolinediones.

A simple cumene (isopropylbenzene, IPB) promoted auto-oxidation involved tandem radical cyclization of N-methacryloyl benzamides using stable and easy-to-handle CBr4 as the bromine source is described. This strategy provides an efficient and practical approach for the synthesis of bromine containing isoquinolinediones. This method also presents a new way to generate bromine radicals using a mild auto-oxidation pathway.

Air promoted annulation of thiophenols with alkynes leading to benzothiophenes.

Air promoted intermolecular annulation of thiophenols with alkynes, leading to complex benzothiophenes, is reported. This atom-economical reaction is performed in the absence of any catalyst, chemical oxidant and additive. Only a solvent and an air atmosphere were required. A plausible radical involved mechanism is proposed.

Auto-oxidation promoted sp3 C-H arylation of glycine derivatives.

An auto-oxidation promoted sp3 C-H arylation reaction between N-aryl glycine derivatives and electron-rich arenes, leading to the formation of N-aryl α-aryl α-amino acid derivatives, is described. This atom-economical and environmentally benign reaction proceeds smoothly under mild reaction conditions and requires only Brønsted acid and oxygen (balloon). A plausible radical involved mechanism is proposed.

One-Pot Synthesis of ß-Hydroxysulfones and Its Application in the Preparation of Anticancer Drug Bicalutamide.

An efficient one-pot multistep strategy has been developed, comprising auto-oxidative difunctionalization of alkenes, oxidation of sulfides, and a further reduction of peroxides for the synthesis of complex ß-hydroxysulfone derivatives from phenthiols and alkenes. This method has several advantageous characteristics, including readily available substrates, low-cost and environmental benign reagents, nontoxic and renewable solvents, and mild reaction conditions. The application of this transformation to the multigram-scale preparation of the anticancer drug bicalutamide is accomplished.

Tandem radical cyclization to construct poly-brominated 2-oxindoles.

Catalytic amounts of TBHP (15 mol%) promoted tribromomethylation of activated alkenes has been developed. This method provided a metal-free aerobic way to construct tribromomethylated 2-oxindoles from the reaction of readily available N-arylacrylamides with CBr4via a proposed tandem radical cyclization process. Air is used as an efficient terminal oxidant in this transformation. The formation of 1,1-dibromoolefin derivatives was also realized at higher temperature under neat conditions.

CBr4 promoted intramolecular aerobic oxidative dehydrogenative arylation of aldehydes: application in the synthesis of xanthones and fluorenones.

A simple and practical carbon tetrabromide promoted intramolecular aerobic oxidative dehydrogenative coupling reaction has been developed to provide a straightforward ring closure protocol for 2-aryloxybenzaldehydes to furnish xanthones. The reaction was performed under metal-, additive- and solvent-free conditions with good tolerance of functional groups. The present method is also applicable to the synthesis of fluorenones by using 2-arylbenzaldehydes as substrates. Preliminary studies of the reaction mechanism indicated that the reaction may proceed through a radical pathway.

CBr4-mediated cross-dehydrogenative coupling reaction of amines.

A novel CBr4-mediated dehydrogenative Povarov/aromatization tandem reaction of glycine derivatives with alkenes, leading to complex quinoline derivatives, and a CBr4-mediated dehydrogenative C-H functionalization of N-aryl tetrahydroisoquinolines with nucleophiles to form C-C and C-P bonds are reported. The reactions were performed under very simple and mild reaction conditions; only CBr4 was used as a promoter. A plausible mechanism involving a radical process is proposed.

Brønsted Acid-Catalyzed Three-Component Reaction of Anilines, α-Oxoaldehydes, and α-Angelicalactone for the Synthesis of Complex Pyrrolidones.

A green and efficient three-component reaction of easily available anilines, α-oxoaldehydes, and α-angelicalactone was developed for the synthesis of highly functionalized pyrrolidones using dilute sulfuric acid as the catalyst. Products were obtained in good to high yields at room temperature and under solvent-free conditions. The reaction could also be performed on a multigram scale with the same efficiency.

Radical Cation Salt-Promoted Catalytic Aerobic sp(3) C-H Oxidation: Construction of Quinoline-Fused Lactones and Lactams.

A direct construction of quinoline-fused lactones and lactams was achieved by sp(3) C-H bond oxidation of N-aryl glycine esters and amides under catalytic radical cation salt-induced conditions. These polycyclic products are formed in a single step from readily accessible starting materials, and this method provides a new synthetic approach to this class of heterocycles.