Palladium and radical routes to phenanthridines

Bowman, W. Russell; Lyon, Jessica E.; Pritchard, Gareth J.

doi:10.3998/ark.5550190.0013.714

Cited by 8 publications

(4 citation statements)

References 5 publications

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“…Precursors of the biphenylethanone O -dialkylcarbamoyl oxime type (e.g., 8a ), which contain volatile amine moieties, were convenient starting points for phenanthridine syntheses. Other routes to this ring system include anionic processes, Pd-catalyzed cross-coupling reactions, and radical-mediated processes; , the latter two approaches have recently been reviewed . Our strategy is promising for preparations of this and other types of N-heterocycles in terms of ease of precursor preparation, mild and metal-free experimental procedure, and easy workup.…”

Section: Discussionmentioning

confidence: 99%

Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime Carbamates

McBurney

Walton

2013

J. Am. Chem. Soc.

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A set of oxime carbamates having N-alkyl and N,N-dialkyl substituents were prepared via carbonyldiimidazole intermediates. It was shown by EPR spectroscopy that they underwent clean homolysis of their N–O bonds upon UV photolysis. During photolysis of acetophenone O-allylcarbamoyl oxime, the corresponding oxazolidin-2-onylmethyl radical was detected by EPR spectroscopy, providing the first evidence that N-monosubstituted carbamoyloxyl radicals can hold their structural integrity. N,N-Disubstituted carbamoyloxyl radicals dissociated rapidly at the lowest accessible temperatures. Above room temperature, both types of oxime carbamate acted as selective new precursors for aminyl and iminyl radicals. Rate parameters were measured for 5-exo cyclization of N-benzyl-N-pent-4-enylaminyl radicals; the rate constant was smaller than for C-centered and O-centered analogues. Oxime carbamates derived from the volatile diethylamine afforded aryliminyl radicals that proved convenient for phenanthridine preparations.

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Section: Discussionmentioning

confidence: 99%

Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime Carbamates

McBurney

Walton

2013

J. Am. Chem. Soc.

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“…Because of their ready availability and high stability, amides are a class of very attractive starting materials in organic synthesis. 13 However, the high stability renders the direct transformation of amides quite challenging, which requires either harsh reaction conditions, 11f 14 15a or multistep transformations, 15b or a lack of functional group tolerance/chemoselectivity, or being limited in scope. 14 This is the case of the Morgan–Walls reaction 14a that involves the dehydrative cyclization of acyl- o -xenylamines in refluxing neat phosphorus oxychloride (POCl 3 ) (Scheme 1, 1 ), which failed with formyl- o -xenylamine.…”

Section: Table 1 Screening Of Reaction Conditions ...mentioning

confidence: 99%

Tf2O-Promoted Morgan–Walls Reaction: From a Flexible Approach to Functionalized Phenanthridines and Quinazolines to the Short and Divergent Total Syntheses of Alkaloids

Huang

2022

Synthesis

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A new protocol for the direct transformation of secondary amides (N-acyl-o-xenylamines) into phenanthridines under mild conditions is reported. The method features trifluoromethanesulfonic anhydride (Tf2O)/2-fluoropyridine as the efficient amide activation system and MeCN or CH2Cl2 as the solvent. For some substrates, MeCN participated in the reaction, which affords a mild access to polysubstituted quinazolines. By employing the Tf2O/2,4,6-tri-tert-butylpyrimidine (TTBP) combination, the method was extended to an N-formyl-o-xenylamine, which represents a recalcitrant amide substrate type for the dehydracyclization reaction. More importantly, a one-pot method was established for the direct and divergent synthesis of four types of phenanthridinoids from o-xenylamines, which features both tert-N-formyl-o-xenylamines and phenanthridinium salt as key and versatile intermediates. The investigation resulted in one of the shortest and the most efficient total syntheses of three natural products: trisphaeridine, 5,6-dihydrobicolorine, N-methylcrinasiadine, and in the formal total syntheses of other three ones: 3-hydroxytrisphaeridine, bicolorine, and zephycandidine A.

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“…Figure displays pioneering examples of radical-based synthesis of phenanthridines via intramolecular cyclization of imidoyl radical intermediates . In 1985, Leardini et al reported hydrogen abstraction of biarylimines generating imidoyl radicals, which were converted into the corresponding phenanthridines via intramolecular cyclization and hydrogen abstraction (Figure a) . As precursors of imidoyl radicals leading to phenanthridines, 2-isocyano-1,1′-biphenyls have also been utilized …”

Section: Introductionmentioning

confidence: 99%

“… 6 In 1985, Leardini et al reported hydrogen abstraction of biarylimines generating imidoyl radicals, which were converted into the corresponding phenanthridines via intramolecular cyclization and hydrogen abstraction ( Figure 2 a). 7 As precursors of imidoyl radicals leading to phenanthridines, 2-isocyano-1,1′-biphenyls have also been utilized. 8 Figure 2 b shows the radical isonitrile insertion process reported by Nanni et al involving the AIBN-derived 2-cyanopropyl radical.…”

Section: Introductionmentioning

confidence: 99%

Difluoromethylborates and Muonium for the Study of Isonitrile Insertion Affording Phenanthridines via Imidoyl Radicals

Konagaya,

Huang,

Iwami

et al. 2023

J. Org. Chem.

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The 6-(difluoromethyl)phenanthridine unit is a highly attractive fluoroalkyl-substituted planar nitrogen heterocycle in pharmaceutical and agrochemical research. In this paper, we report that difluoromethylborates can be used as a source of difluoromethyl radicals for isonitrile insertion, leading to 6-(difluoromethyl)phenanthridines. Tuning the aryl substituents in the difluoromethylborates and oxidizing reagents enabled the synthesis of 6-(difluoromethyl)phenanthridines through the generation of difluoromethyl radical and spontaneous intramolecular cyclization of the CF 2 H-imidoyl radical intermediates. The presence of difluoromethyl radicals was experimentally confirmed, and the reaction mechanisms including imidoyl radical and prompt cyclization reactions could be supported theoretically. Furthermore, we obtained valuable information about the imidoyl radical intermediate by performing transverse-field muon spin rotation (TF-μSR) measurements of 2-isocyano-4′-methoxy-1,1′-biphenyl and using density functional theory (DFT) calculations to interpret the spectra. Muonium, a simple free radical, preferentially adds to the carbon atom of the isonitrile unit, yielding the corresponding imidoyl radical. The temperature dependence of the muon hyperfine coupling constant and the spin relaxation of the muoniated radical signal are compatible with the intramolecular cyclization of biaryl-substituted imidoyl radicals on the μs time scale.

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Palladium and radical routes to phenanthridines

Abstract: Two routes to phenanthridines are reported; a palladium-mediated route using imidoyl-selanides as precursors and a modified radical route using aryl imines as starting materials.

Cited by 8 publications

References 5 publications

Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime Carbamates

Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime Carbamates

Tf2O-Promoted Morgan–Walls Reaction: From a Flexible Approach to Functionalized Phenanthridines and Quinazolines to the Short and Divergent Total Syntheses of Alkaloids

Difluoromethylborates and Muonium for the Study of Isonitrile Insertion Affording Phenanthridines via Imidoyl Radicals

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