title: Fast Equilibrium in N-(Ethoxycarbonyl)-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-ones in Flattened Boat Conformations.
abstract: The preferred conformations of three N-ethoxycarbonyl derivatives of r-2,c-7-diphenylhexahydro-1,4-diazepin-5-ones 9-11 have been studied using NMR spectral techniques. The N(1),N(4)-bis(ethoxycarbonyl)-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-ones 9 and 10 were found to prefer flattened boat conformations with fast equilibrium between two N-CO rotamers while 4-(ethoxycarbonyl)-t-3-isopropyl-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-one (11) was found to prefer a chair conformation with the N-COOEt group locked in one rotameric state. Dynamic (1)H NMR studies have been carried out on the N(1),N(4)-bis(ethoxycarbonyl) derivatives 9 and 10, and the barriers for the N-CO rotation were found to be 49.9 and 58.0 kJ mol(-1), respectively. These barriers are much lower than those observed for N-nitroso- and N-formyl-r-2,c-7-diphenylhexahydro-1,4-diazepin-5-ones (90.0 and 84.4 kJ mol(-1), respectively), indicating a fast equilibrium in 9 and 10 at room temperature.
authors.affiliation: Department of Chemistry, Bharathidasan University, Tiruchirappalli-620 024, India.
authors.forename: Ramasubbu
authors.initials: R
authors.lastname: Jeyaraman
authors.forename: Subbu
authors.initials: S
authors.lastname: Ponnuswamy