Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1402782 | Journal of Molecular Structure | 2014 | 7 Pages |
•1,5-Benzodiazepines from o-phenylenediamines and dehydroacetic acid is discussed.•Difficulties of characterizing the prototropy of 1,5-benzodiazepines were discussed.•The presence of the (E)-amino-en-one tautomer of 1,5-benzodiazepines A was confirmed.•Theoretical calculations, NMR data and especially single-crystal X-ray diffraction were used.
The synthesis of 1,5-benzodiazepines by the reaction of o-phenylenediamines (o-PDAs) with dehydroacetic acid DHAA [3-acetyl-4-hydroxy-6-methyl-2H-pyran-2-one] or conjugate analogues is largely reported in the literature, but still with uncontrolled stereochemistry. In this work, a comprehensive mechanistic study on the formation of some synthesized 1,5-benzodiazepine models following different organic routes is established based on liquid-state 2D NMR, single-crystal X-ray diffraction and theoretical calculations allowing the classification of two prototropic forms A (enaminopyran-2,4-dione) and B (imino-4-hydroxypyran-2-one). Evidences are presented to show that most of the reported 1,5-benzodiazepine structures arising from DHAA and derivatives preferentially adopt the (E)-enaminopyran-2,4-diones A.
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