Molecular, electronic structure and conformational flexibility of the 1,6-dihydropyrimidine, 4,5-dihydrofuro[2,3-d]pyrimidine and their oxo, imino and methylene derivatives

Molecular and electronic structures of 1,6-dihydropyrimidine, 4,5-dihydrofuro[2,3-d]pyrimidine and their oxo, imino and methylene derivatives have been studied using the semiempirical quantum-chemical method AM1. The equilibrium geometry of all molecules is planar. These results were confirmed by X-...

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Bibliographic Details
Published in:Journal of molecular structure 1996-11, Vol.385 (1), p.55-63
Main Authors: Shishkin, Oleg V., Antonov, Dmitry M.
Format: Article
Language:English
Subjects:
AM1
Conformational analysis
Dihydrofuropyrimidine
Dihydropyrimidine
Ylide derivative
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Summary:Molecular and electronic structures of 1,6-dihydropyrimidine, 4,5-dihydrofuro[2,3-d]pyrimidine and their oxo, imino and methylene derivatives have been studied using the semiempirical quantum-chemical method AM1. The equilibrium geometry of all molecules is planar. These results were confirmed by X-ray structural investigations of the 1-oxo- and 1-imino derivatives of 2,5-dimethyl-3-(2,2,2-trichloroethyl)-4,5-dihydrofuro[2,3-d]pyrimidine. However, the dihydropyrimidine ring in all compounds possesses a degree of conformational flexibility. The transition from a planar equilibrium conformation to a distorted sofa with the CNCC torsion angle ± 20° causes an increase of energy less than 1.5 kcal mol −1. The factors that determine this property of the dihydroheterocycle (bending strain, non-aromaticity, conjugation, 1,2-allylic strain) have been considered.
ISSN:0022-2860
1872-8014
DOI:10.1016/S0022-2860(96)09345-3