Synthesis, characterisation, conformational preferences, dynamic NMR studies and antimicrobial evaluation of N-nitroso- and N-formyl-c-3,t-3-dimethyl-r-2,c-7-diphenyl-1,4-diazepan-5-ones

• N-nitroso- and N-formyl-1,4-diazepan-5-ones were synthesized.
• Assignment of 1H & 13C NMR signals are made using 2D NMR spectra.
• N-nitroso-1,4-diazepan-5-one prefers chair conformation with diaxial phenyl groups.
• X-ray crystal structure of N-nitroso compound has been solved.
• Energy barriers for N–NO & N–CO rotations are calculated using dynamic NMR spectra.

The stereochemical preferences of N-nitroso- and N-formyl-c-3,t-3-dimethyl-r-2,c-7-diphenyl-1,4-diazepan-5-ones 3 & 4, respectively, have been determined using 1D and 2D NMR spectral techniques. Interestingly, the N-nitroso compound 3 is found to prefer an equilibrium between alternate chair conformations with diaxial phenyl groups, while the N-formyl compound 4 prefers flattened boat conformation. This is stereochemically a novel report on the flexible rings adopting a chair conformation with diaxial phenyl groups. The X-ray crystal structure of N-nitroso-c-3,t-3-dimethyl-r-2,c-7-diphenyl-1,4-diazepan-5-one (3) also supports the chair conformation with diaxial phenyl groups. Dynamic 1H NMR spectral studies have been carried out on the N-nitroso and N-formyl diazepan-5-ones 3 & 4 and the energy barriers for N–NO and N–CO rotations are found to be 88.7 and 75.7 kJ/mol, respectively. The antimicrobial activities have been determined for the compounds 2–4 and it is found that all the compounds exhibit significant antibacterial and antifungal activities when compared to the standard chloramphenicol.

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