Hayashi rearrangement

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The Hayashi rearrangement is a name reaction from organic chemistry . It was named after the Japanese chemist Mosuke Hayashi (1895–1990), who first reported on it in 1927. During the reaction, a rearrangement reaction of the o- benzoylbenzoic acid takes place through acidification with sulfuric acid .

Overview reaction

The Hayashi rearrangement of ortho- benzoylbenzoic acid at a glance:

Overview of the Hayashi rearrangement

General

The reaction takes place at 173–175 ° C and requires concentrated sulfuric acid as a catalyst . Catalysts other than phosphorus pentoxide show no effect on rearrangement. The reaction occurs only in relatively rare cases, so it is only of particular use for the preparation of special derivatives. Similar reactions take place with naphthalenes and diphenylmethanes .

Proposed reaction mechanism

In the following reaction mechanism, the gray arrows stand for a rotation around the axis on which they are set and the red arrows for electron migration. First of all, the marked connection in FIG. 1 must be rotated so that the spatial relationship in reaction 3 becomes conclusive. In 2 there is a nucleophilic addition of the proton to the carbonyl group of the ketone , resulting in Figure 3 . Due to a lack of electrons, the electron pair of the carbonyl group folds to the oxygen and a carbocation is created , which is sterically attacked by the OH group of the carboxylic acid as a nucleophile . Connection 4 is created . The reactive intermediate stages that follow are explicitly put in square brackets because they are unstable and only have a very short lifespan. The H + and the left aryl group are simultaneously split off from 4 , whereby the electron pair of the aryl group forms a bond to the H + . As a result, the transition state 5 arises , which due to the charge causes electron migration and leads to constitution 6 . In Figures 6 and 7 , only the position of the molecule is corrected. The now electrophilic addition in 8 takes place in a degrading manner through the OH group on the benzene ring in the ortho position . The exact reaction mechanism now shows that the right benzene ring is split off with the ketone and a new bond is made through the carboxy group .

Hayashi rearrangement reaction

literature

  • Zerong Wang: Comprehensive Organic Name Reactions and Reagents, Volume 2, Wiley, 2009, pp. 1347-1349, ISBN 978-0-471-70450-8
  • The Merck Index, 9th Edition, Merck & Co. 1976, ONR-41, ISBN 0911910-26-3

Individual evidence

  1. ↑ MG Zolotukhin, FJ Balta Calleja, DR Rueda, M. Bruix, Yu. L. Sorokina, EA Sedova: Macromolecules . tape 28 , 1995, pp. 7325-7330 , doi : 10.1021 / ma00126a006 .
  2. ^ A b Zerong Wang: Comprehensive Organic Name Reactions and Reagents, Volume 2, Wiley, 2009, pp. 1347 f., ISBN 978-0-471-70450-8 .