Standard Article

The Pschorr Synthesis and Related Diazonium Ring Closure Reactions

  1. DeLos F. DeTar

Published Online: 15 MAR 2011

DOI: 10.1002/0471264180.or009.07

Organic Reactions

Organic Reactions

How to Cite

DeTar, D. F. 2011. The Pschorr Synthesis and Related Diazonium Ring Closure Reactions. Organic Reactions. 9:7:409–462.

Author Information

  1. University of South Carolina

Publication History

  1. Published Online: 15 MAR 2011

Chemistry Terms

Choose one or more boxes to highlight terms.


In the middle 1890s, three groups of chemists independently discovered a new cyclization reaction of certain appropriately constituted diazonium salts. Fischer and Schmidt reported that an aqueous solution of 2-benzylbenzenediazonium chloride furnished fluorene on heating. Graebe and Ullman reported that 2-benzoylbenzenediazonium chloride yielded fluorenone and Staedel reported a somewhat similar result from the action of nitrous acid on 2,2'-diaminbenozpehnone, a reaction that produced a little 1-hydroxyfluorenone. Two years later, Robert Pschorr applied the ring closure reaction to the diazonium salt derived from trans-2-amino-alpha-phenylcinnamic acid to obtain phenanthrene-9-carboxylic acid. The principal utility of these cyclizations reactions has been the synthesis of substituted ring structures in which the positions of the substituents are known.


  • Pschorr synthesis;
  • diazonium ring closures. Bridge;
  • side reactions;
  • simultaneous ring closures;
  • aliphatic analogs;
  • cyclization;
  • Gomberg-Bachmann synthesis