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EnglishBy means of DFT and AIM calculations, the steric and stereoelectronic effects that control the enantioselectivity in the cross-aldol addition of acetone to isatin catalysed by L-proline have been studied. This reaction results in a reversal of enantioselectivity when compared with the corresponding cross-aldol addition to 4,6-dibromoisatin and to aldehydes. DFT calculations of the cross-aldol transition states indicate that product formation follows different pathways for the substrates isatin and 4,6-dibromoisatin. In the case of isatin, the S-enantiomer is favoured as a consequence of a stereoelectronic effect that results in a lower energy transition state for the S-enantiomer relative to the R- enantiomer. In contrast, the cross-aldol addition of acetone to 4,6-dibromoisatin furnishes the expected R-enantiomer due to a steric effect of the 4-bromo substituent which inhibits formation of the S-enantiomer via the stereoelectronically favoured transition state.
| Titolo: | A DFT and AIM study of the proline catalysed asymmetric cross-aldol addition of acetone to isatins: a rationalization for the reversal of chirality |
| Autore/i: | R. J. Corrêa; S. J. Garden; ANGELICI, GAETANO; TOMASINI, CLAUDIA |
| Autore/i Unibo: | |
| Anno: | 2008 |
| Rivista: | |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.1002/ejoc.200700944 |
| Abstract: | By means of DFT and AIM calculations, the steric and stereoelectronic effects that control the enantioselectivity in the cross-aldol addition of acetone to isatin catalysed by L-proline have been studied. This reaction results in a reversal of enantioselectivity when compared with the corresponding cross-aldol addition to 4,6-dibromoisatin and to aldehydes. DFT calculations of the cross-aldol transition states indicate that product formation follows different pathways for the substrates isatin and 4,6-dibromoisatin. In the case of isatin, the S-enantiomer is favoured as a consequence of a stereoelectronic effect that results in a lower energy transition state for the S-enantiomer relative to the R- enantiomer. In contrast, the cross-aldol addition of acetone to 4,6-dibromoisatin furnishes the expected R-enantiomer due to a steric effect of the 4-bromo substituent which inhibits formation of the S-enantiomer via the stereoelectronically favoured transition state. |
| Data prodotto definitivo in UGOV: | 2008-02-26 14:38:14 |
| Appare nelle tipologie: | 1.01 Articolo in rivista |
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http://hdl.handle.net/11585/57595
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