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  • Title: Diazocinones: synthesis and conformational analysis.
    Author: Robins LI, Carpenter RD, Fettinger JC, Haddadin MJ, Tinti DS, Kurth MJ.
    Journal: J Org Chem; 2006 Mar 17; 71(6):2480-5. PubMed ID: 16526800.
    Abstract:
    1,2,4,5-Tetrazines (prepared from aryl nitriles) condense with isoxazolylcyclobutanones (prepared from 3-benzenesulfonyl-3-vinylcyclobutanol) in methanolic KOH to give conformationally restricted 6-isoxazol-5-yl-6,7-dihydro-5H-[1,2]diazocin-4-ones. The solution 1H NMR spectra of dihydrodiazocinone 1a with phenyl moieties at C3 and C8 reveal two conformations of the eight-membered heterocycle that are non-interconverting on the NMR time scale at ambient temperature. The kinetics of the conversion process, followed by 1H NMR between 21 and 70 degrees C in DMSO solution, yield an activation energy of approximately 21 kcal/mol relative to the kinetic conformer and show an equilibrated ratio of approximately 5:1 of the thermodynamic to the kinetic conformers. The electronic structure calculations on a model dihydrodiazocinone predict geometries for the two conformations. One of these geometries agrees with the X-ray crystallographic analysis of the thermodynamic conformation of 1a.
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