Bucherer carbazole synthesis

Carbazoles from naphthols and aryl hydrazines promoted by sodium bisulfite. 

Bucherer, H. T. J. Prakt. Chem. 1904, 69, 49. Hans Th. Bucherer (1869—1949) was bom in Ehrenfeld, Germany. He shuttled between industry and academia all through his career. 

Seeboth, H. Barwolff, D. Becker, B. Justus Liebigs Ann. Chem. 1965, 683, 85. 

Robinson, B. The Fischer Indole Synthesis, Wiley-Interscience, New York, 1982. (Book). 

Transformation of p-naphthols to p-naphthylamines using ammonium sulfite. 

Gilbert, E. E. Sulfonation and Related Reactions Wiley New York, 1965, pi66. (Review). 

The Bucherer carbazole synthesis involves the treatment of a naphthyl alcohol (1 or 4) or a naphthyl amine (2 or 5) with a phenylhydrazine 3 in the presence of aqueous sodium bisulfite to afford, after acidic work-up, either a benzo[a]carbazole 4 or benzo[c]carbazole 6. 

The Bucherer carbazole synthesis was first demonstrated when 7 was heated in the presence of phenylhydrazines 8, sodium hydroxide and sodium bisulfite after acidic work-up, the benzocarbazole product 9 was isolated (-70% yield). When 2-naphthol was used the reaction was significantly slower with the yield of benzocarbazole being only 46% after several days at 130 °C Bucherer and co-workers investigated this reaction extensively concluding, incorrectly, that intermediate products were probably carbazole-Al-sulfonic acids due to the ease with which they lost the sulfonic acid residues to yield benzocarbazoles. 

Whereas the similarity between the Bucherer carbazole synthesis and the Fischer indolisation was noted by Bucherer and Seyde in their pioneering work, it was only later 

When naphthyl amines e.g. 23) are used in the Bucherer carbazole synthesis, they are converted by the catalytic action of aqueous bisulfite into tetralonesulfonic acid derivative 13 by the Bucherer reaction. Addition of NaHSOs gives an enamine, which tautomerises to the imine 24 24 is hydrolysed to keto form 13 and subsequent Bucherer carbazole synthesis follows to afford the benzocarbazole product 20.  

The Bucherer carbazole synthesis is, to a certain extent, limited by the availabilty of the starting naphthol and naphthylamine reagents. However, a variety of substituents have been used and these are illustrated for the conversion of 25 to 27. The use of 2-aminoanthracene in the Bucherer carbazole synthesis has also been demonstrated.  

Carbazole formation from naphthols and aryl hydrazines promoted by sodium bisulfite. Another variant of the Fiseher indole synthesis. 

Name Reactions, 4th ed., DOI 10.1007/978-3-642-01053-8 36, Springer-Verlag Berlin Heidelberg 2009 

Bucherer carbazole synthesis. In Name Reactions in Heterocyclic Chemistry, Li, J. J., Corey, E. J., Eds. Wiley Sons Hoboken, NJ, 2005, pp 110—115. (Review). 

Name Reactions A Collection of Detailed Mechanisms and Synthetic Applications, DOI 10.1007/978-3-319-03979-4 41, Springer International Publishing Switzerland 2014 

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The Bucherer carbazole synthesis was pivotal in the preparation of the first hexahelicene 37a. Reaction of 2,7-dihydroxynaphthalene 35 with phenylhydrazine and sodium bisulfite afforded helicene 37a although in low yield. More recently, the synthesis was extended to the preparation of 37b using 2,5-dimethylphenylhydrazine 36b. ... 

See this general concept in the Fischer Indole Synthesis and the Bucherer Carbazole Synthesis. 

Bucherer carbazole synthesis. Formation of carbazoles from naphthols or naphthylamines, aryl-hydrazines, and sodium bisulfite. 

This reaction is related to the Bucherer Carbazole Synthesis, Fischer Indole Synthesis, Graebe-Ullmann Synthesis and Piloty-Robinson Pyrrole Synthesis. 

This reaction was first reported by Bucherer in 1906. It is the synthesis of carbazoles from aryl hydrazines, sodium bisulfite, and 1- or 2-naphthols (or 1- or 2-naphthylamines) and is generally known as the Bucherer carbazole synthesis or Bucherer reaction. In addition, the reaction between 2-aminonaphthalene-l-sulfonic acid and phenylhydrazine also gives carbazole, indicating that sulfonation of naphthylamine might be the early step in the reaction pathway. This reaction has been most commonly used hitherto for the preparation of dibenzocarboles. ... 

Other references related to the Bucherer carbazole synthesis are cited in the literature. ... 

The Bucherer carbazole synthesis is the reaction of aromatic phenols, typically naphthols, with phenylhydra-zine to form the corresponding phenylhydrazone via the naphthol tautomer [150, 151]. Bucherer was an early... 

A.J. Moore (2005) Bucherer carbazole synthesis, in Name Reactions in Heterocyclic Chemistry (ed. J.J. Li), Wiley Sons, Hoboken, New Jersey, pp 110-115. 

Bucherer Carbazole Synthesis Bucherer Reaction Bucherer-Bergs Reaction Biichi (see Patemo-Biichi Reaction)... 

N. Campbell, B. M. Barclay, Chem. Rev. 40, 361 (1947) W. Freudenberg, Heterocyclic Compounds 3, 298 (1952) P. Bruck, J. Org. Chem. 35,2222 (1970). Cf. Bucherer Carbazole Synthesis Fischer Indole Synthesis Pilotv-Robinson Synthesis. 

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