Paternò-Büchi reaction

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The Paternò-Büchi reaction is a photochemical [2 + 2] cycloaddition named after Emanuele Paternò and George Hermann Büchi for the formation of four-membered oxetane rings from a carbonyl component and an alkene .

Overview reaction

In the example, acetone reacts with 2,3-dimethylbut-2-ene under the action of light to form hexamethyloxetane ( 1 ):

Paterno-Büchi reaction symmetrical

The substituents on the alkene and the carbonyl component determine the stereochemistry of the products, so the reaction of benzaldehyde (Ph = phenyl radical ) with 2-methylbutene produces a mixture of the two structurally isomeric oxetanes 2a and 2b :

Paterno-Büchi reaction asymmetrical

mechanism

The reaction is initiated by irradiation with long-wave UV light, which only excites the carbonyl compound. The carbonyl compound ( aldehyde or ketone ) reacts with the alkene in concert or via a diradical stage. Olefins with electron-withdrawing substituents prefer a concerted mechanism, while donor substituents favor a radical mechanism, whereby the diradicals can be detected by trapping reactions.

application

The reaction is used in the synthesis of natural products, but has only limited importance because of its often low selectivity.

literature

  • E. Paternò, G. Chieffi: Sintesi in chimica organica per mezzo della luce. Nota II. Composti degli idrocarburi non saturi con aldeidi e chetoni. In: Gazz. Chim. Ital. , 39, 1909, pp. 341-361.
  • G. Büchi, Charles G. Inman, and ES Lipinsky: Light-catalyzed Organic Reactions. I. The Reaction of Carbonyl Compounds with 2-Methyl-2-Butene in the Presence of Ultraviolet Light . In: Journal of the American Chemical Society . 76, No. 17, 1954, pp. 4327-4331. doi : 10.1021 / ja01646a024 .

Individual evidence

  1. ↑ Thorsten Bach: Stereoselective Intermolecular [2 + 2] -Photocycloaddition Reactions and Their Application in Synthesis . In: Synthesis . 1998, 1998, pp. 683-703. doi : 10.1055 / s-1998-2054 .
  2. ↑ László Kürti and Barbara Czakó .: Strategic Applications of Named Reactions in Organic Synthesis: Background and Detailed Mechanisms , Elsevier Academic Press, 2005, pp. 332–333, ISBN 978-0-12-429785-2 .

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