Isoinversion principle

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The isoinversion principle is a model developed by Hans-Dieter Scharf at RWTH Aachen University for diagnosing, optimizing and predicting selectivity in asymmetric syntheses. It is a dynamic model in which all selectivity-relevant parameters for planning and optimizing the selectivity-determining step of a chemical reaction are taken into account. The model can also be used to confirm or refute a mechanistic guess.

The principle is a deductive method and is based on the measurement of the temperature dependence of selected selectivity parameters such as e.g. B. steric hindrance on selectivity. The so-called isoinversion temperature can be determined from the kinetic data based on the Eyring theory. The principle describes kinetically controlled reactions that show a temperature-dependent change in the rate-determining step.

Fig. 1 Kinetic approach of the isoinversion principle

The underlying kinetic scheme is applicable not only to stoichiometric reactions, but also to catalytic reactions. At a first selection level (see Fig. 1), two diastereomeric intermediates are formed from the prochiral starting material B and the chiral substrate E *, {E * B} 1 and {E * B} 2 . On a second level there is competition between the formation of the products P 1 * and P 2 * and the reversion into the starting materials E * and B. By varying the temperature, the stereoselectivity can either be increased or increased, depending on the constructive or destructive interaction of the two selection levels to be humiliated. Experimentally, a non-linear Eyring plot is observed if there is a temperature-dependent change in the rate-determining step in the temperature window investigated.

The method can be applied to different types of selectivity such as enantio-, diastereo-, regio-, chemoselective reactions.

The principle was developed when Scharf investigated the temperature dependence of the Paternò-Büchi reaction and found a non-linear dependence of the diastereoselectivity on the temperature.

Individual evidence

  1. ^ Helmut Buschmann, Hans-Dieter Scharf, Norbert Hoffmann, Peter Esser: The Isoinversion Principle - a General Model of Chemical Selectivity. In: Angewandte Chemie International Edition in English. 30, 1991, pp. 477-515, doi : 10.1002 / anie.199104771 .
  2. ^ Helmut Buschmann, Hans Dieter Scharf, Norbert Hoffmann, Martin Wolfgang Plath, Jan Runsink: Chiral induction in photochemical reactions. 10. The principle of isoinversion: a model of stereoselection developed from the diastereoselectivity of the Paterno-Buechi reaction. In: Journal of the American Chemical Society. 111, 1989, pp. 5367-5373, doi : 10.1021 / ja00196a048 .

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