2,3-Difunctionalized Indoles via Radical Acylation or Trifluoromethylation of ortho-Alkynylphenyl Isonitriles

Thermal and Photoinduced Radical Cascade Annulation using Aryl Isonitriles: An Approach to Quinoline-Derived Benzophosphole Oxides

Herein, we present a radical cascade addition cyclization sequence to access quinoline-based benzophosphole oxides from ortho-alkynylated aromatic phosphine oxides using various aryl isonitriles as radical acceptors and inexpensive tert-butyl-hydroperoxide (TBHP) as a terminal oxidant in the presence of a catalytic amount of silver acetate. Alternatively, the same cascade can be realized through a sustainable photochemical approach utilizing 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as an organic photocatalyst at room temperature. The introduced modular approach shows broad functional group tolerance and offers straightforward access to complex P,N-containing polyheterocyclic arenes. These novel π-extended benzophosphole oxides exhibit interesting photophysical and electrochemical properties such as absorption in the visible region, emission and reversible reduction at low potentials, which makes them promising for potential materials science applications. The photophysical properties can further be tuned by the addition of external Lewis and Brønsted acids.

Three-Component Domino Reaction of Thioamide, Isonitriles, and Water: Selective Synthesis of 1,2,4-Thiadiazolidin-3-ones and (E)-N-(1,2-Diamino-2-thioxoethylidene)benzamides

The three-component domino reaction of thioamides, benzyl isocyanide, and water in the presence of a catalytic amount of both Pd(dppf)Cl2 and Cu(OAc)2 afforded novel 1,2,4-thiadiazolidin-3-one cyclic compounds, whereas the same reaction with tertiary alkylisonitriles in the presence of rare earth metal salt [La(OTf)3] resulted in (E)-N-(1,2-diamino-2-thioxoethylidene)benzamide open-chain products. This divergent reaction enabled the one-pot construction of five (N-S, C-S, C-O, and two C-N) or four (C-S, C-N, C-O, and C-C) new chemical bonds. Mechanism studies indicate that the oxygen atom of the product was derived from H2O.

Synthesis of 2,4-Dicyanoalkylated Benzoxazines through the Radical-Mediated Cascade Cyclization of Isocyanides with AIBN under Metal- and Additive-Free Conditions

A general and novel method for the radical cascade cyclization of aryl isocyanides with AIBN has been described. This strategy provides straightforward access to various 2,4-dicyanoalkylated benzoxazines in moderate to good yields under metal- and additive-free conditions. The reaction can apply to a gram scale and tolerate diverse functional groups. 2,4-Dicyanoalkylated benzoxazine derivatives feature a large Stokes shift and intramolecular charge transfer properties.

Photocatalytic cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones for the construction of quinoxalino[2,1-b]quinazolinones

A new kind of building unit, 3-(2-isocyanophenyl)quinazolin-4(3H)-ones, was designed and synthesized for the construction of novel quinoxalino[2,1-b]quinazolinones. The radical cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones with ethers afforded ether-substituted tetracyclic quinoxalino[2,1-b]quinazolinones under photocatalytic and metal-free conditions. In the process, the isocyano accepts a carbon radical to give an imidoyl radical, which adds to the electron-deficient CN bond in quinazolin-4(3H)-one.

Access to Polyheterocyclic Compounds through Iron(II)-Mediated Radical Cascade Cyclization Utilizing 2-Ethynylbenzaldehydes and Aryl Isonitriles

An oxidative radical cascade addition cyclization approach for the synthesis of quinoline-based π-extended polyheterocyclic compounds is reported. Eco-friendly iron catalysis and inexpensive tert-butylhydroperoxide (TBHP) as the oxidant have been utilized in the transformation of various readily available ortho-alkynylated aromatic aldehydes as radical precursors with aryl isonitriles as radical acceptors. Indole and thiophene-based carbaldehydes allow the preparation of quinolines that are π-conjugated with an additional heteroarene moiety in a single sequence by applying the introduced method.

Bicyclic Amidine-Triggered Cyclization of o-Alkynylisocyanobenzenes: Synthesis of Lactam-Derived Quinolines

Efficient access to the synthesis of lactam-derived quinoline through a bicyclic amidine-triggered cyclization reaction from readily prepared o-alkynylisocyanobenzenes has been developed. The reaction was initiated by nucleophilic attack of the bicyclic amidines to o-alkynylisocyanobenzenes, subsequently with intramolecular cyclization to produce a DBU-quinoline-based amidinium salt, followed by hydrolysis to afford the lactam-derived quinoline in moderate to good yields.

Enantioselective Copper-Catalyzed Fukuyama Indole Synthesis from 2-Vinylphenyl Isocyanides

Enantioenriched chiral indoles are of high interest for the pharmaceutical and agrochemical industries. Herein, we present an asymmetric Fukuyama indole synthesis through a mild and efficient radical cascade reaction to access 2-fluoroalkylated 3-(α-cyanobenzylated) indoles by stereochemical control with a chiral copper-bisoxazoline complex using 2-vinylphenyl arylisocyanides as radical acceptors and fluoroalkyl iodides as C-radical precursors. Radical addition to the isonitrile moiety, 5-exo-trig cyclization, and Cu-catalyzed stereoselective cyanation provide the targeted indoles with excellent enantioselectivity and good yields. Due to the similar electronic and steric properties of the two aryl substituents to be differentiated, the enantioselective construction of the cyano diaryl methane stereocenter is highly challenging. Mechanistic studies reveal a negative nonlinear effect which allows proposing a model to explain the stereochemical outcome. Scalability and potential utility of the enantioenriched 3-(α-cyanobenzylated) indoles as hubs for chiral tryptamines, indole-3-acetic acid derivatives, and triarylmethanes are demonstrated, and a formal synthesis of a natural product analogue is disclosed.

Electrochemical trifluoromethylation of 2-isocyanobiaryls using CF3SO2Na: synthesis of 6-(trifluoromethyl)phenanthridines

An efficient trifluoromethylation of 2-isocyanobiaryls was developed through the constant current electrolysis, employing sodium trifluoromethanesulfinate (CF₃SO₂Na) as the trifluoromethyl source. The method enabled the syntheses of a series of 6-(trifluoromethyl)phenanthridine derivatives in moderate to high yields under metal- and oxidant-free conditions. A gram-scale synthesis highlights the synthetic versatility of the reported protocol.

Mn(III)-Mediated Radical Addition/Cyclization of Isocyanides with Aryl Boronic Acids/Diarylphosphine Oxides: Access to 11-Functionalized Dibenzodiazepines

A Mn(III)-mediated radical addition/cyclization reaction of isocyanides with aryl boronic acids/diarylphosphine oxides has been developed. A series of 11-arylated/-phosphorylated dibenzodiazepines were efficiently constructed in moderate to excellent yields under mild reaction conditions via imidoyl radical process. The present protocol offers novel access to functionalized seven-membered N-heterocycles.

Tetrabutylammonium Chloride-Induced Cascade Radical Addition/Cyclization of O-Isocyanodiaryl Amines: A Novel Protocol for the Synthesis of 11-Trifluoromethylated Dibenzodiazepines

A straightforward protocol for the synthesis of 11-trifluoromethylated dibenzodiazepines has been developed via TBAC-induced trifluoromethylation/cyclization of o-isocyanodiaryl amines using Togni's reagent as the trifluoromethyl source. This is the first report on the one-step construction of CF₃-containing dibenzodiazepine drug skeletons. Additionally, a series of 11-trifluoromethylated dibenzodiazepines were afforded in moderate to excellent yields under transition-metal-free conditions.

Recent Advances in Transition-Metal Mediated Trifluoromethylation Reactions

Fluorine compounds are known for their abundance in more than 20% of pharmaceutical and agrochemical products mainly due to the enhanced lipophilicity, metabolic stability and pharmacokinetic properties of organofluorides. Consequently,...