Expedient green-chemistry approaches for one-pot synthesis of two series of novel 1,5-benzodiazepines via domino reactions
Unique green-chemistry approaches have been developed for the one-pot synthesis of two series of novel 1,5-benzodiazepines 4 and 5. The CeCl3-KI promoted two-component domino reaction of 1,2-phenylenediamines with 1,3-acetonedicarboxylate in ethanol afforded novel 1,5-benzodiazepin-2-ones 4. An expedient approach to 1,5-benzodiazepines 5 has also been developed via three-component domino reactions using 1,2-phenylenediamines, 1,3-acetonedicarboxylate and aldehydes in the presence of a catalytic amount of magnetic nanoparticles (γ-Fe2O3@SiO2/CeCl3) in ethanol at ambient temperature. During the above one-pot synthesis process, one new seven-membered nitrogen heterocycle (diazepin) and four new bonds (one C–C, two C–N and one C=C) were constructed by the nucleophilic addition, elimination reaction (dehydration etc.), hydride transfer and cyclization process. Structures of all 48 products were fully confirmed by spectroscopic techniques and by single-crystal X-ray analysis of 5db. Moreover, plausible synthesis reaction mechanisms of two series of novel 1,5-benzodiazepines 4 and 5 have been proposed. The methods have advantages such as operational simplicity, mild reaction conditions, short reaction time, easy recovery and reusability of the catalyst, high yields of products, and non-toxic EtOH as the solvent.