Controlled Synthesis of α-CF2H or α-CF2Cl Styrenes from the Same Precursors: Dehydrazinative Hydrogenation or Chlorination of 3,3-Difluoroallyl Hydrazines.

By carefully choosing the reaction conditions, we have developed the controllable FeCl3- or CuCl2-mediated dehydrazinative hydrogenation or chlorination of 3,3-difluoroallyl hydrazines to access α-CF2H or α-CF2Cl styrenes. The current reaction provides for the first time a facile method for the direct and selective synthesis of α-CF2H and α-CF2Cl styrenes starting from the same precursors, which is easy to scale up and displays a broad substrate scope and good functional group tolerance. Moreover, product derivatization experiments demonstrated that the resulting α-CF2Cl styrenes are practical and versatile building blocks for the diversified synthesis of fluorinated molecules.

Silver-Catalyzed Cascade Cyclization of Amino-NH-1,2,3-Triazoles with 2-Alkynylbenzaldehydes: An Access to Pentacyclic Fused Triazoles.

An operationally simple Ag(I)-catalyzed approach for the synthesis of isoquinoline and quinazoline fused 1,2,3-triazoles was developed by a condensation and amination cyclization cascade of amino-NH-1,2,3-triazoles with 2-alkynylbenzaldehydes involving three new C-N bond formations in one manipulation, in which the group of -NH of the triazole ring serves as a nucleophile to form the quinazoline skeleton. The efficient protocol can be applied to a variety of substrates containing a range of functional groups, delivering novel pentacyclic fused 1,2,3-triazoles in good-to-excellent yields.

Doyle-Kirmse reaction using 3,3-difluoroallyl sulfide and N-sulfonyl-1,2,3-triazole: an efficient access to gem-difluoroallylated multifunctional quaternary carbon.

A Doyle-Kirmse reaction of N-sulfonyl-1,2,3-triazole with 3,3-difluoroallyl sulfide through a Rh(ii)-catalyzed [2,3]-sigmatropic rearrangement has been developed, which provides an efficient access to multifunctional quaternary centers containing aryl, imino, thio, and brominated gem-difluoroallyl groups. The reaction features broad substrate scope with moderate to excellent yields. The applicability of the method is confirmed by gram-scale synthesis and further transformations.

Copper-catalyzed cross-coupling and sequential allene-mediated cyclization for the synthesis of 1,2,3-triazolo[1,5-a]quinolines.

In this paper, a tandem reaction involving copper-catalyzed cross-coupling and allene-mediated cyclization of 1-(2-ethynylaryl)-1,4-disubstituted-1,2,3-triazole with N-tosylhydrazone has been developed. This method features operational simplicity, excellent functional group compatibility, broad substrate scope, and easily available feedstock, providing an efficient and practical strategy for the synthesis of highly functionalized 1,2,3-triazolo[1,5-a]quinolines.

gem-Difluoroallylation of Aryl Diazoesters via Catalyst-Free, Blue-Light-Mediated Formal Doyle-Kirmse Reaction.

A first example of low-energy blue-light-mediated formal Doyle-Kirmse reaction for gem-difluoroallylation of aryl diazoesters has been developed. A variety of highly functionalized gem-difluoroallyl containing esters bearing transformable sulfur and bromine groups were efficiently assembled with broad substrate scope under mild, catalyst-free, and additive-free conditions. The reaction represents a practical and environmentally friendly approach for C-CF2 bond formation based on rearrangement strategy, which will find potential applications among drug discovery and development.

Blue light-promoted cross-coupling of aryldiazoacetates and diazocarbonyl compounds.

A blue light-promoted cross-coupling of two distinct diazo compounds was described. The reaction produces E-configured trisubstituted alkenes in good yields in the absence of catalysts and additives. The reactive free carbene intermediates were generated via selective photolysis of one of the two diazo compounds upon blue light irradiation.

Synthesis of 3-Aryl-2-pyrones by Palladium-Catalyzed Cross-Coupling of Aryl Iodides with Cyclic Vinyldiazo Ester.

A palladium-catalyzed cross-coupling reaction of aryl iodides with cyclic vinyldiazo ester was developed. The reaction provides various 3-aryl-2-pyrones in good yields with high functional group tolerance. The synthetic application of the resulting 3-aryl-2-pyrones as the diene component in a Diels-Alder reaction was also described.

Visible-Light-Mediated Two-Fold Unsymmetrical C(sp3 )-H Functionalization and Double C-F Substitution.

A visible-light-mediated [3+3] annulation of tertiary amines with α-trifluoromethyl alkenes was developed. The reaction offers a direct route to fluorinated tetrahydropyridines and azabicyclo[3.m.1] frameworks under very mild conditions. This protocol presents a rare example of dual sp3 C-H functionalization of tertiary amines with the formation of two different C-C bonds (one sp3 -sp3 bond, one sp2 -sp3 bond). Moreover, two consecutive C-F substitutions in a trifluoromethyl group were achieved in one pot using visible light photoredox catalysis, which enables an unprecedented ring construction.

Synthesis of Functionalized gem-Difluoroalkenes via a Photocatalytic Decarboxylative/Defluorinative Reaction.

A photocatalytic decarboxylative/defluorinative reaction of α-trifluoromethyl alkenes with α-keto acids and α-amino acids has been developed. The reaction occurs at room temperature under visible light irradiation, affording various γ,γ-difluoroallylic ketones and 1,1-difluorohomoallyl amines in good yields. The synthetic applications of the resulting functionalized gem-difluoroalkenes were also described.

Synthesis of Gem-Difluorinated Fused Quinolines via Visible Light-Mediated Cascade Radical Cyclization.

A facile synthesis of gem-difluorinated fused quinolines via visible light-mediated cascade radical cyclization between functionalized difluoromethyl chlorides and alkenes was developed. Various highly functionalized fused quinolines were assembled in moderate to good yields under very mild reaction conditions. The reaction extends the applications of chlorodifluoroacetic acid as the gem-difluoromethylenated building block by simple derivatization, especially in the synthesis of gem-difluorinated fused heterocyclic rings, which are difficult to access with existing methods.

Synthesis of N-Containing Heterocyclic Compounds Using Visible-light Photoredox Catalysis.

Nitrogen heterocycles represent a highly important class of compounds which are widely used in materials science, agrochemistry, and medicinal chemistry. Therefore, there is continuing interest in the development of convenient, efficient, and environmentally benign synthetic methods for the construction of nitrogen containing heterocycles. Due to its natural abundance, ease of use, and promising application in industry, the use of visible light as a driving force for chemical reactions has received considerable attention in the past few years. This account summarizes the synthesis of N-heterocycles using visible-light photoredox catalysis published in the last two years, according to the size and type of the formed N-heterocyclic rings. In the context of seminal works of others in this area, a concise summary of the contributions of the authors is also offered.

Ag(I)-Catalyzed Three-Component Reaction of 2-Alkynylbenzaldehydes, Amines, and Diazo Compounds.

Diazo compounds have been employed as the nucleophile in a silver-catalyzed three-component reaction with amines and 2-alkynylbenzaldehydes. Various 3-benzazepines were prepared in a one-pot manner based on a cascade imine--yne cyclization/nucleophilic addition/1,2-aryl migration process. Moreover, this Ag(I)-mediated reaction also provides a practical route to diazo-containing dihydroisoquinolines under slightly modified conditions.

Metal-free visible-light induced cross-dehydrogenative coupling of tertiary amines with diazo compounds.

The first visible-light induced cross-dehydrogenative coupling between tertiary amines and diazo compounds is described. The reaction proceeds smoothly under mild and metal-free conditions by using air or O2 as the oxidant, affording various ß-amino-α-diazo adducts in moderate to good yields with broad substrate scopes. The resulting products were successfully employed for the synthesis of 4- or 5-ester N-aryl-2,3-dihydrobenzo[d]azepines with high regioselectivity simply switched by the selection of the transition metal catalysts.

CuI-catalyzed cross-coupling of terminal alkynes with dialkoxycarbenes: a general method for the synthesis of unsymmetrical propargylic acetals.

A general source of dialkoxycarbenes, 2,2-dialkoxy-5,5-dimethyl-Δ(3)-1,3,4-oxadiazolines, have been successfully employed as coupling partners in CuI-catalyzed cross-coupling reactions with terminal alkynes, which afforded various unsymmetrical propargylic acetals in good yields.

Synthesis of 3-acylindoles by visible-light induced intramolecular oxidative cyclization of o-alkynylated N,N-dialkylamines.

A visible-light photoredox synthesis of 3-acylindoles through intramolecular oxidative cyclization of o-alkynylated N,N-dialkylamines is developed. The reaction proceeds effectively under mild reaction conditions using air as the oxidant, and only water is generated as a side product. A plausible mechanism involving the addition of α-amino alkyl radicals to alkynes, followed by C-O bond formation, is proposed.

PhI(OAc)2-mediated synthesis of 6-(trifluoromethyl)phenanthridines by oxidative cyclization of 2-isocyanobiphenyls with CF3SiMe3 under metal-free conditions.

A mild and efficient method for the synthesis of 6-(trifluoromethyl)phenanthridines through oxidative cyclization of 2-isocyanobiphenyls with CF3SiMe3 under metal-free conditions was developed. The reaction allows the direct formation of C-CF3 bonds and rapid access to phenanthridine ring systems in one catalytic cycle.

Benzofuran and indole synthesis via Cu(I)-catalyzed coupling of N-tosylhydrazone and o-hydroxy or o-amino phenylacetylene.

A general and practical method to synthesize 2-substituted benzofurans and indoles is described. This method employs easily accessible N-tosylhydrazones and o-hydroxy or o-amino phenylacetylenes as substrates. The reaction proceeds through a CuBr-catalyzed coupling-allenylation-cyclization sequence under ligand-free conditions.