Abstract

Aziridines are widely used as versatile building blocks for the synthesis of a variety of biologically and pharmaceutically importantmolecules [1]. Among the available methodologies for the preparation of functionalised aziridines, the lithiation/trapping sequence of simpleparent aziridines is growing in importance [2]. Present work reports the results concerning the structural study of aziridine-2-methanolderivatives by dynamic nuclear magnetic resonance (DMNR) [3] and single crystal X-ray diffraction. A careful examination of the aziridine2 (see figure 1) by NMR data, shows that at room temperature the meta protons and the protons of the two ortho methyl groups of the mesitylring gives featureless lumps, likely as consequence of a restricted rotation around the Csp3 -Csp2 bond between the carbinolic carbon andthe ipso carbon of the mesityl ring. Also in the solid state, an almost identical arrangement of the mesityl ring, with respect to the other twophenyl rings, has been observed. In this case, the aziridine nitrogen substituent was found in a syn relationship with respect to the carbinolicgroup so preventing the possibility of forming a hydrogen bond with the hydroxyl group. This evidence underlines a slow rotation of themesityl group instead of a nitrogen inversion as usually is expected. By X-ray analysis of 3 and diast-3 (figure 1), it is estimated that thenitrogen substituents set on the opposite side with respect the carbinolic carbon. Via study of crystal structures, the presence of hydrogenbonds between the hydroxyl group and the aziridine nitrogen lone pair was ascertained for aziridine 3 but not for diast-3 (figure 1). Such a hydrogen bond, which is persistent also in solution, could prevent the formation of conformational diastereoisomers by rotation around the bond between the carbinolic carbon and the aziridine quaternary carbon. This hypothesis has been demonstrated by NMR experiments. This investigation allowed us to calcolate some Csp2-Csp3 and Csp3-Csp3 rotational barriers and highlight a sort of "geared" rotation between aryl and alkyl substituents; this is possible if the structure is not in a locked conformation by an hydrogen bond as demonstrated by NMR and X-ray diffraction.

Autore Pugliese

• Altomare Angela , Moliterni Anna , Falcicchio Aurelia , Cuocci Corrado , Rizzi Rosanna

Tutti gli autori

• A. Falcicchio; A. Altomare; C. Cuocci; R. Luisi; A. Moliterni ; R. Rizzi

Titolo volume/Rivista

Acta crystallographica. Section A, Crystal physics, diffraction, theoretical and general crystallography

Anno di pubblicazione

2011

ISSN

1600-8596

ISBN

Non Disponibile

Numero di citazioni Wos

Nessuna citazione

Ultimo Aggiornamento Citazioni

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Numero di citazioni Scopus

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Ultimo Aggiornamento Citazioni

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Settori ERC

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Codici ASJC

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