Dakin–West reaction

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Not to be confused with Dakin reaction.

The Dakin–West reaction is a chemical reaction that transforms an amino-acid into a keto-amide using an acid anhydride and a base, typically pyridine. It is named for Henry Drysdale Dakin (1880–1952) and Randolph West (1890–1949). In 2016 Schreiner and coworkers reported the first asymmetric variant of this reaction employing short oligopeptides as catalysts.

The Dakin–West reaction
The Dakin–West reaction

With pyridine as a base and solvent, refluxing conditions are required. However, with the addition of 4-dimethylaminopyridine (DMAP) as a catalyst, the reaction can take place at room temperature.

With some acids, this reaction can take place even in the absence of an α-amino group.

This reaction should not be confused with the Dakin reaction.

Reaction mechanism

The reaction mechanism involves the acylation and activation of the acid 1 to the mixed anhydride 3. The amide will serve as a nucleophile for the cyclization forming the azlactone 4. Deprotonation and acylation of the azlactone forms the key carbon-carbon bond. Subsequent ring-opening of 6 and decarboxylation give the final keto-amide product.

The mechanism of the Dakin-West reaction
The mechanism of the Dakin-West reaction

General ketone synthesis

Modern variations on the Dakin–West reaction permit many enolizable carboxylic acids – not merely amino acids – to be converted to their corresponding methyl ketones. For example, β-aryl carboxylic acids can be efficiently converted to β-aryl ketones by treatment of an acetic anhydride solution of the acid with catalytic N-methylimidazole. This reactivity is attributed in part to generation of acetylimidazolium, a powerful cationic acetylating agent, in situ.

Modified Dakin-West reaction
Modified Dakin-West reaction

See also

References

  1. ^ Dakin, Henry Drysdale; West, Randolph (1928). "A General Reaction of Amino Acids". The Journal of Biological Chemistry. 78 (1): 91–104. doi:10.1016/S0021-9258(18)84021-2.
  2. ^ Dakin, Henry Drysdale; West, Randolph (1928). "A General Reaction of Amino Acids. II". The Journal of Biological Chemistry. 78 (3): 745–756. doi:10.1016/S0021-9258(18)83978-3.
  3. ^ Dakin, Henry Drysdale; West, Randolph (1928). "Some Aromatic Derivatives of Substituted Acetylaminoacetones". The Journal of Biological Chemistry. 78 (3): 757–764. doi:10.1016/S0021-9258(18)83979-5.
  4. ^ Wiley, Richard H. (1947). "The Conversion of Amino Acids to Oxazoles". The Journal of Organic Chemistry. 12 (1): 43–46. doi:10.1021/jo01165a006. PMID 20280736.
  5. ^ Buchanan, G. L. (1988). "The Dakin–West reaction". Chemical Society Reviews. 17: 91–109. doi:10.1039/CS9881700091.
  6. ^ Wende, Raffael C.; Seitz, Alexander; Niedek, Dominik; Schuler, Sören M. M.; Hofmann, Christine; Becker, Jonathan; Schreiner, Peter R. (2016). "The Enantioselective Dakin-West Reaction". Angewandte Chemie International Edition. 55 (8): 2719–2723. doi:10.1002/anie.201509863. PMID 26804727.
  7. ^ Wiley, Richard H.; Borum, O. H. (1953). "3-Acetamido-2-butanone". Organic Syntheses. 33: 1. doi:10.15227/orgsyn.033.0001.
  8. ^ Höfle, Gerhard; Steglich, Wolfgang; Vorbrüggen, Helmut (1978). "4-Dialkylaminopyridines as Highly Active Acylation Catalysts. ". Angewandte Chemie International Edition in English. 17 (8): 569–583. doi:10.1002/anie.197805691.
  9. ^ Knorr, Rudolf; Huisgen, Rolf (1970). "Zum Mechanismus der Dakin-West-Reaktion, I Die Reaktion von N-Acyl-sek.-aminosäuren mit Acetanhydrid". Chemische Berichte. 103 (8): 2598–2610. doi:10.1002/cber.19701030831. PMID 5448834.
  10. ^ Allinger, Norman L.; Wang, Grace L.; Dewhurst, Brian B. (1974). "Kinetic and mechanistic studies of the Dakin-West reaction". The Journal of Organic Chemistry. 39 (12): 1730–1735. doi:10.1021/jo00925a029.
  11. ^ Tran, Khanh-Van; Bickar, David (2006). "Dakin−West Synthesis of β-Aryl Ketones". The Journal of Organic Chemistry. 71 (17): 6640–6643. doi:10.1021/jo0607966. PMID 16901161.
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