Unusual behavior in the reactivity of 5-substituted-1<i>H</i>-tetrazoles in a resistively heated microreactor

Gutmann, Bernhard; Glasnov, Toma N.; Razzaq, Tahseen; Goessler, Walter; Roberge, Dominique M.; Kappe, C. Oliver

doi:10.3762/bjoc.7.59

Cited by 26 publications

(12 citation statements)

References 58 publications

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“…The authors have subsequently utilised a flow reactor to investigate the decomposition of 5-benzhydryl-1H-tetrazole to diphenylmethane, employing a reaction temperature of 220 • C and a residence time of 10 min. 26 Jensen and Zaborenko 27 concurrently reported the use of a silicon micro mixer (volume = 4.1 ml) for the two-step synthesis of the highly energetic sodium nitrotetrazole, gaining access to the material at an impressive throughput of 4.4 g h -1 .…”

Section: Principle 2 Atom Economymentioning

confidence: 99%

Continuous flow reactors: a perspective

2012

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Section: Principle 2 Atom Economymentioning

confidence: 99%

Continuous flow reactors: a perspective

2012

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“…Similarly, the catalytic efficiency and metal leaching in a palladium coated or “palladated” stainless steel coil was evaluated by Kappe and co‐workers for the Mirozoki‐Heck reaction of 4‐iodobenzonitrile and butyl acrylate (Table 2). 61 To investigate this phenomena in more detail a 16 mL stainless steel coil was “palladated” by processing 2 mL of a reaction mixture containing 1 mol % Pd(OAc) 2 through the coil. The coil was then thoroughly washed with MeCN at 170 °C and utilized for a fresh reaction in which no additional catalyst was used.…”

Section: Transition Metal‐catalyzed Cross Couplings In Continuous mentioning

confidence: 99%

Immobilized Transition Metals as Catalysts for Cross‐Couplings in Continuous Flow—A Critical Assessment of the Reaction Mechanism and Metal Leaching

2014

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In the not too distant future many industrially important chemicals (including pharmaceuticals) will probably be manufactured using continuous flow technology. For a significant number of synthetic steps involved in these protocols transition metal (mostly palladium)‐catalyzed carbon–carbon or carbon–heteroatom bond forming reactions (“cross‐coupling chemistry”) will play an important role. Designing a process for continuous cross‐coupling chemistry involves either the use of a homogeneous or of a heterogeneous (immobilized) catalyst/ligand system. In the latter case, the catalyst/ligand system is typically in the form of a packed‐bed reactor, through which the reaction mixture is pumped, employing an appropriate temperature regime and residence time. Although this approach has been widely popular during the past 15 years, there is growing evidence that suggests that the use of immobilized transition metal catalysts for performing cross‐coupling chemistry in continuous flow is, in fact, not very practical. As demonstrated in this review, significant leaching of the transition metal out of the packed‐bed catalyst will almost inevitably occur, leading to decreased catalyst activity and contamination of the product with transition metal. This is a consequence of the well‐known fact that the reaction mechanism for these kinds of transformations is (quasi)homogeneous and involves the transformation of a Pd0 species into a (soluble) PdII species. Using an immobilized catalyst in a batch protocol the transient leaching of palladium will not be immediately obvious, as, after completion of the catalytic cycle, Pd0 will typically redeposit onto the support. In contrast, in continuous flow mode, the palladium metal will progressively be “chromatographed” through the packed‐bed catalyst until, ultimately, all palladium will be removed from the support. This effect typically will become only evident when long run experiments are performed. The preferred alternative, in particular for larger scale experiments, is to use a homogeneous (pre)catalyst in combination with an appropriate catalyst recycling technology.

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“…The conversion was completed within 8 min as determined by TLC, but surprisingly no trace of the desired tetrazole 11 was detected by LC–MS. We presume that the tetrazole was unstable under the applied reaction conditions [ 66 ]. Tetrazole derivative 11 was alternatively obtained in excellent yield and purity by refluxing nitrile 12 with sodium azide and ammonium chloride in DMF, followed by treatment with bromine to yield the corresponding brominated tetrazole 10 in excellent yield and high purity (see Scheme 3 , Table 1 ).…”

Section: Resultsmentioning

confidence: 99%

Syntheses of 2-substituted 1-amino-4-bromoanthraquinones (bromaminic acid analogues) – precursors for dyes and drugs

Malik¹,

Müller²

2015

Beilstein J. Org. Chem.

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SummaryAnthraquinone (AQ) derivatives play a prominent role in medicine and also in textile industry. Bromaminic acid (1-amino-4-bromoanthraquinone-2-sulfonic acid) is an important precursor for obtaining dyes as well as biologically active compounds through the replacement of the C4-bromo substituent with different (ar)alkylamino residues. Here we report methods for the synthesis of bromaminic acid analogues bearing different substituents at the 2-position of the anthraquinone core. 1-Aminoanthraquinone was converted to its 2-hydroxymethyl-substituted derivative which, under different reaction conditions, yielded the corresponding carbaldehyde, carboxylic acid, and nitrile derivatives. The latter was further reacted to obtain 1-amino-2-tetrazolylanthraquinone. Subsequent bromination using bromine in DMF led to the corresponding bromaminic acid derivatives in excellent isolated yields (>90%) and high purities. Alternatively, 1-amino-4-bromo-2-hydroxymethylanthraquinone could be directly converted to the desired 2-substituted bromaminic acid analogues in high yields (85–100%). We additionally report the preparation of bromaminic acid sodium salt and 1-amino-2,4-dibromoanthraquinone directly from 1-aminoanthraquinone in excellent yields (94–100%) and high purities. The synthesized brominated AQs are valuable precursors for the preparation of AQ drugs and dyes.

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Unusual behavior in the reactivity of 5-substituted-1H-tetrazoles in a resistively heated microreactor

Cited by 26 publications

References 58 publications

Continuous flow reactors: a perspective

Continuous flow reactors: a perspective

Immobilized Transition Metals as Catalysts for Cross‐Couplings in Continuous Flow—A Critical Assessment of the Reaction Mechanism and Metal Leaching

Syntheses of 2-substituted 1-amino-4-bromoanthraquinones (bromaminic acid analogues) – precursors for dyes and drugs

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