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Regiospecific Synthesis and Structural Studies of 3,5-Dihydro-4 H -pyrido[2,3- b ][1,4]diazepin-4-ones and Comparison with 1,3-Dihydro-2 H -benzo[ b ][1,4]diazepin-2-ones

Abstract : Nine 3,5-dihydro-4H-pyrido[2,3-b][1,4]diazepin-4-ones (17−25), some of which contain fluoro-substituents, have been regiospecifically prepared by reaction of 2,3-diaminopyridines with ethyl aroylacetates. In two cases, open intermediates have been isolated and these are related to the reaction pathway. The X-ray crystal structure of 1-methyl-4-phenyl-3,5-dihydro-4H-pyrido[2,3-b][1,4]diazepin-4-one (23) has been solved (formula, C 15 H 13 N 3 O; crystal system, monoclinic; space group, C2/c). This is an asymmetric unit constituted by a single nonplanar molecule and its conformational enantiomer due to the presence of the seven-membered diazepin-2-one moiety, which introduces a certain degree of torsion in the adjacent pyridine ring. The 1 H, 13 C, 15 N, and 19 F NMR spectra were obtained and the chemical shifts, together with those of the previously published 1,3-dihydro-2H-benzo[b][1,4]diazepin-2-ones (1−16), i.e., a total of 544 values, were successfully compared with the chemical shifts calculated at the gauge invariant atomic orbital (GIAO)/Becke, three-parameter, Lee−Yang−Parr (B3LYP)/6-311++G(d,p) level. The seven-membered ring inversion barrier in 5-benzyl-2-phenyl-3,5-dihydro-4H-pyrido[2,3b][1,4]diazepin-4-one (25) was determined and, in conjunction with the data from the literature, compared with the B3LYP/6-311+ +G(d,p) computed values. This allowed the determination of several structural effects. The rotation about the exocyclic N1−CR bond was also calculated and its dynamic properties were discussed.
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Submitted on : Tuesday, March 23, 2021 - 6:41:57 PM
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David Nunez Alonso, Marta Perez-Torralba, Rosa M. Claramunt, Carmen Torralba, Patricia Delgado-Martinez, et al.. Regiospecific Synthesis and Structural Studies of 3,5-Dihydro-4 H -pyrido[2,3- b ][1,4]diazepin-4-ones and Comparison with 1,3-Dihydro-2 H -benzo[ b ][1,4]diazepin-2-ones. ACS Omega, ACS Publications, 2020, 5 (39), pp.25408-25422. ⟨10.1021/acsomega.0c03843⟩. ⟨hal-03178458⟩



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