Synthesis of 6-Phosphorylated Phenanthridines by Mn(II)-Promoted Tandem Reactions of 2-Biaryl Isothiocyanates with Phosphine Oxides

Mn(II) Promoted Divergent-Convergent Domino Reaction Giving Dinuclear Tetrasubstituted Pyrrole Complex

Domino reaction of benzo[d]thiazole-2-methylamine (S1) has been developed in the presence of MnCl2 ⋅ 4H2O, leading to tetrasubstituted pyrrole coordinated dinuclear Mn(II) complex 1 ([MnClP]2, P-=2,3,4,5-tetrakis(benzo[d]thiazol-2-yl)pyrrol-1-ide). The reaction process has been studied by assigning a series of intermediates based on time-dependent mass spectrometry, control experiments, crystallography, and density functional theory (DFT) theoretical calculation. A plausible mechanism involving an unprecedented divergent-convergent domino sequence has been proposed. Compound S1 could be activated by MnCl2 ⋅ 4H2O via coordination, which divergently produces two intermediates imine II (1-(benzo[d]thiazol-2-yl)-N-(benzo[d]thiazol-2-ylmethyl)methanimine) and alkene C (1,2-bis(benzo[d]thiazol-2-yl)ethene) through oxidative self-condensation and free radical coupling followed by elimination, respectively. They could then react with each other convergently via formal [3+2] cycloaddition to give deprotonated tetrasubstituted pyrrole coordinated intermediate [MnClP] after aromatization. Dimerization of [MnClP] produces the final product 1. Three C-C bonds and one C-N bond are formed through this six-step domino sequence. The corresponding organic skeleton (HP: 2,2',2'',2'''-(1H-pyrrole-2,3,4,5-tetrayl)tetrakis(benzo[d]thiazole)) has been obtained from 1 and shows a higher fluorescent quantum yield (52 %) than the reported 3,4-diphenyl substituted analogue 2,2'-(3,4-diphenyl-1H-pyrrole-2,5-diyl)bis(benzo[d]thiazole) (DPB) (42 %).

Copper(II)-catalyzed cascade Csp2-P/C-C bond formation to construct benzo[d]thiazol-2-ylphosphonates

A novel, copper(II)-catalyzed cascade Csp2-P/C-C bond formation in o-haloaryl isothiocyanates with organophosphorus esters has been developed under mild conditions. A series of benzo[d]thiazol-2-ylphosphonates were synthesized in moderate to good yields. Different from the traditional method of obtaining these scaffolds with radical reactions, the method proposed allows accessing them via ionic reactions and has the advantages of easy access to raw materials and simple operation. Finally, we carried out a gram-scale experiment to further demonstrate the scalability of this strategy in the efficient synthesis of benzo[d]thiazol-2-ylphosphonates.

A Review on Synthetic Approaches of Phenanthridine

Abstract:

The phenanthridine family is widely found in medicinal chemistry and material science because of the biological activity and its presence in a variety of significant natural products and synthetic dye stuffs. The phenanthridine has many clinical applications, for e.g., being used as an anticancer agent, possessing antibacterial, antiprotozoal, pharmaceutical, and optoelectronic properties. Many methods have been reported for the synthesis of phenanthridine and phenanthridine alkaloids, such as Pd catalyzed C-C bond formation, a reaction involving C-H activation, radical, microwave-assisted, transition metal-catalyzed, one-pot cascade, benzyne mediated, photochemical, hypervalent iodine promoted methods, etc. Here, we have summarized the literature data from 2014 to the present concerning novel or improved synthetic approaches.

I2-mediated Csp2–P bond formation via tandem cyclization of o-alkynylphenyl isothiocyanates with organophosphorus esters

A highly efficient molecular-iodine-catalyzed cascade cyclization reaction has been developed, creating a series of 4H-benzo[d][1,3]thiazin-2-yl phosphonates in moderate to excellent yields. This approach benefits from metal-free catalysts and available raw materials.

Base-promoted Cyclization Reaction of o-Isothiocyanato Arylacetylenes and Aroylacetonitriles: Easy Access to Benzo[d][1,3]thiazines

A green and efficient synthesis of benzo[d][1,3]thiazines through base-promoted cyclization reaction of o-isothiocyanato arylacetylenes with aroylacetonitriles has been developed. This protocol displays high step economy and efficiency, and tolerates various...

Excited-state cobaloxime catalysis enabled scalable oxidant-free dehydrogenative C–H phosphinoylation of undirected heterocycles

Visible-light-induced excited-state cobalt catalysis enables C(sp2)–H/C(sp3)–H phosphinoylation accompanied by H2 evolution. The reaction achieves the late-stage modification of more than 10 distinct classes of heterocycles and arenes.

Photocatalytic xanthate-based radical addition/cyclization reaction sequence toward 2-biphenyl isocyanides: synthesis of 6-alkylated phenanthridines

A photocatalytic xanthate-based radical addition/cyclization reaction cascade toward 2-biphenylisocyanides is described as a practical and modular approach to 6-alkylated phenanthridines. The use of xanthates as radical precursors allowed the synthesis of diversely 6-substituted phenanthridines. Electrophilic radicals derived from nitriles, aromatic and aliphatic ketones, malonates, and amide derivatives, as well as radicals derived from phthalimidomethyl and benzylic derivatives were successfully introduced. The reaction proceeds under mild conditions without a stoichiometric amount of oxidant. Thirty novel phenanthridine scaffolds were synthesized with yields ranging from 24 to 76%.

Manganese(iii)-promoted tandem phosphinoylation/cyclization of 2-arylindoles/2-arylbenzimidazoles with disubstituted phosphine oxides

A simple and practical method for the synthesis of phosphoryl-substituted indolo[2,1-a]isoquinolin-6(5H)-ones and benzimidazo[2,1-a]isoquinolin-6(5H)-ones through manganese(iii)-promoted tandem phosphinoylation/cyclization of 2-arylindoles or 2-arylbenzimidazoles with disubstituted phosphine oxides was developed. In this transformation, new C-P bond and C-C bond were constructed simultaneously under silver-free conditions, exhibiting a broad substrate scope. It was noted that not only diarylphosphine oxides but also dialkyl and arylalkyl-phosphine oxides were compatible with the conditions.

A carboxylate-assisted amination/unactivated C(sp2)–H arylation reaction via a palladium/norbornene cooperative catalysis

A carboxylate-assisted palladium-catalysed Catellani reaction, which is compatible with ortho-amination and unactivated C(sp²)–H arylation, synthesized a series of 1-amino substituted dihydrophenanthridines, phenanthridines and 6H-benzo[c]chromenes.

Flexible Synthesis of Phosphoryl-Substituted Imidazolines, Tetrahydropyrimidines, and Thioamides by Sulfur-Mediated Processes

The solvent-free sulfur-mediated reactions of phosphinic chlorides with alkyl diamines were developed for the practical synthesis of unknown phosphoryl-substituted 4,5-dihydro-1H-imidazoles, 1,4,5,6-tetrahydropyrimidines, and thioamides. Their good tolerance to functional groups, broad substrate scope, and easy scalability were shown. The chemoselective preparation of a variety of phosphoryl-substituted bis(thioamides) was accomplished via the adjustment of a solvent.

Visible-light-induced sulfonylation/cyclization of vinyl azides: one-pot construction of 6-(sulfonylmethyl)phenanthridines

A facile and efficient protocol has been developed for sulfonylation/cyclization of vinyl azides under photoredox conditions.

Electrooxidative CH/PH functionalization as a novel way to synthesize benzo[b]phosphole oxides mediated by catalytic amounts of silver acetate

Electrochemical oxidation synthesis of benzo[b]phosphole oxides has been performed at room temperature with catalytic amounts of AgOAc.

Synthesis of 6-(sulfonylmethyl)phenanthridines through a reaction of aryldiazonium tetrafluoroborates, sulfur dioxide, and vinyl azides

Synthesis of 6-(sulfonylmethyl)phenanthridines through a three-component reaction of aryldiazonium tetrafluoroborates, a sulfur dioxide surrogate of DABCO·(SO₂)₂, and vinyl azides under metal- and additive-free conditions is achieved.

Copper-catalyzed decarboxylative cyclization via tandem C–P and C–N bond formation: access to 2-phosphorylmethyl indoles

A copper-catalyzed decarboxylative cyclization of ethynyl benzoxazinanones with P(O)H compounds has been developed for the synthesis of 2-phosphorylmethyl indoles.

Active methylene compounds (AMCs) controlled facile synthesis of acridine and phenanthridine from morita Baylis–Hillman acetate

We carried out simple and facile syntheses of acridines and phenanthridines from MBH acetates of 2-chloro-quinoline-3-carbaldehyde with active methylene compounds (AMCs).