STRUCTURE OF A TRIAZAOXATRICYCLODECADIENE DERIVATIVE - PARTIAL DISORDER AND A PACKING ENERGY STUDY

The crystal structure of ethyl ricyclo[5.3.0.0(2,6)]deca-4-9-diene-8-c arboxylate, C18H21N3O3 (III), has been determined. The reaction betwee n 2,6-dimethylbenzonitrile oxide (I) and ethyl 5-methyl-1,2-diazepine- 1-carboxylate (II) gives rise to an anti tricycle derivative with a ri gid skeleton formed by 2-pyrazoline, cyclobutane and 2-isoxazoline pla nar rings. With respect to the central cyclobutane system, the bond le ngths of which range from 1.539 (5) to 1.558 (5) Angstrom and the bond angles of which range from 89.7 (2) to 90.7 (2)degrees, the 2-pyrazol ine and the 2-isoxazoline planes form dihedral angles of 116 and 112 d egrees, respectively. The methyl group at the end of the ethyl carboxy late chain is disordered. Both of the corresponding orientations of th e final part of the chain are consistent with the results of packing e nergy and semi-empirical molecular-orbital calculations.