Doetz reaction

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The Dötz reaction is a name reaction of organic chemistry and named after its discoverer Karl Heinz Dötz . The reaction is used for benzoannulation. As starting materials are chromium carbene complexes , alkynes and carbon monoxide (CO) is required.

Overview of the Dötz reaction

mechanism

The reaction begins with the cleavage of a carbonyl ligand from the chromium complex to form the carbene complex 2 . This step determines the rate of the entire reaction, as was found in studies under a CO atmosphere. In the next step , an alkyne adds to the complex in a [2 + 2] cycloaddition to form a chroma cyclobutene 3 . The vinyl carbene complex 4 is then formed by opening the cyclobutene ring . By CO insertion, the ketene 5 is formed , to which the chromium complex is coordinated via the two double bonds formed . In the next step, the ring closure takes place, whereby the ketone 6 is formed. The compound is flavored by keto-enol tautomerism . The chromium complex remaining on the aromatic can now be removed, for example, by reaction with carbon monoxide to form chromium hexacarbonyl (Cr (CO) 6 ). A CO pressure of around 50 bar is necessary for this. Ultimately, the naphthol derivative 7 is obtained in this way.

Overview of the Dötz reaction

application

The Dötz reaction is used in natural product synthesis . For example, vitamins E ( tocopherol ) and K can be synthesized using the Dötz reaction as a key step. The application of the Dötz reaction is also favored by the simple synthesis of the Fischer carbenes required .

Individual evidence

  1. ↑ Karl Heinz Dötz: Synthesis of the Naphthol Skeleton from Pentacarbonyl- [methoxy (phenyl) carbene] chromium (O) and Tolan. In: Angewandte Chemie International Edition in English. 14, No. 9, 1975, pp. 644-645, doi : 10.1002 / anie.197506442 .
  2. ^ Karl Heinz Dötz, Robert Dietz, Alexander von Imhof, Hans Lorenz, Gottfried Huttner: Reactions of complex ligands, IV. Stereoselective synthesis of substituted naphthalenes: Representation and structure of a tricarbonyl (naphthalene) chromium (0) complex. In: Chemical Reports. 109, No. 6, 1976, pp. 2033-2038, doi : 10.1002 / cber.19761090610 .
  3. ↑ Joseph M. Timko, Ayako Yamashita: Synthesis of 2-Substituted Naphthalenediol Derivatives using Chromium Carbene Complexes: 1-Acetoxy-2-Butyl-4-Methoxynaphthalene In: Organic Syntheses . 71, 1993, p. 72, doi : 10.15227 / orgsyn.071.0072 ; Coll. Vol. 9, 1998, p. 1 ( PDF ).
  4. ^ László Kürti , Barbara Czakó: Strategic Applications of Named Reactions in Organic Synthesis . Elsevier Academic Press, Burlington / San Diego / London 2005, ISBN 0-12-369483-3 .