Cyclic Carbodiimides in Nitrene Rearrangements

Wentrup, Curt; Thetaz, Celestin; Tagliaferri, Enrico; Lindner, Hans Jörg; Kitschke, Brigitte; Winter, Hans‐Wilhelm; Reisenauer, Hans Peter

doi:10.1002/anie.198005661

Cited by 22 publications

(14 citation statements)

References 6 publications

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“…The formation of aminobenzoxazole 7 , although in small amounts, is mechanistically fascinating (Schemes and ). The aminonitrilium ion C formed after two sequential Schmidt reactions could intramolecularly interact with the oxygen atom attached to the ring to generate an oxonium ion D (lacking detailed structural information, we have drawn the two limiting stereoisomeric forms of C , while recognizing the possible existence of a linear carbodiimidium cation form) . Subsequent hydration of benzylic carbocation E eventually leads to 7 .…”

Section: Resultsmentioning

confidence: 99%

Remodeling and Enhancing Schmidt Reaction Pathways in Hexafluoroisopropanol

et al. 2016

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The effect of carrying out two variations of the Schmidt reaction with ketone electrophiles in hexafluoroisopropanol (HFIP) solvent has been studied. When TMSN3 is reacted with ketones in the presence of triflic acid (TfOH) promoter, tetrazoles are obtained as the major products. This observation is in contrast to established methods, which usually lead to amides or lactams arising from formal NH insertion as the major products. The full product profiles of several examples of this reaction are also reported and found to include mechanistically interesting products (e.g., double ring expansion). Application of TfOH promoter in HFIP was also found to promote the reaction of a hydroxyalkyl azide with a ketone, which affords lactams following nucleophilic opening of initially formed iminium ether more efficiently than previously reported methods.

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Section: Resultsmentioning

confidence: 99%

Remodeling and Enhancing Schmidt Reaction Pathways in Hexafluoroisopropanol

et al. 2016

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“…In 1980, Reisenauer and coworkers reported the cyclization of carbodiimide compounds by rearrangement of nitrenes to give indolo [2,3-b]quinoxalines in good yields. 14 Indolo [2,3-b]quinoxalines could also be prepared by cyclization of o-phenylenediamine with 1-acetyl-2bromo-3-indolinone. 15 In general, the synthesis of highly functionalized indolo [2,3-b]quinoxalines is difficult, because starting materials are not readily available.…”

Section: Papermentioning

confidence: 99%

Palladium catalyzed synthesis and physical properties of indolo[2,3-b]quinoxalines

et al. 2014

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A series of indolo[2,3-b]quinoxaline derivatives were efficiently synthesized from 2,3-dibromoquinoxaline by two pathways. A one-pot approach using Pd-catalyzed two-fold C-N coupling and C-H activation reactions gave indolo[2,3-b]quinoxaline derivatives in good yields, but with limited substrate scope. In addition, a two-step approach to indolo[2,3-b]quinoxalines was developed which is based on Pd-catalyzed Suzuki coupling reactions and subsequent annulation by Pd-catalyzed two-fold C-N coupling with aromatic and aliphatic amines. The electrochemical and photochemical properties of indolo[2,3-b]quinoxaline derivatives were investigated. These studies show that 6-(4-methoxyphenyl)-6H-indolo[2,3-b]quinoxaline showed the highest HOMO energy level and lowest band gap.

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“…6 For instance, 2-pyridylnitrene 4, generated from 2-azidopyridine or the isomeric tetrazolopyridine, yields didehydro-1,3-diazepine 5 (a cyclic carbodiimide) upon photolysis in an Ar matrix. 7 A variety of heteroaromatic aryl nitrenes could be characterized by EPR, 8 and in some instances also by IR spectroscopy. 6 The products isolated following thermolysis 9 or photolysis 10 of azido-s-triazines in solution exclusively arise from reactions of the triplet or singlet nitrenes.…”

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confidence: 99%