Unusual thermolysis of aza-cyclic allene under microwave conditions: crystal structure of (3RS,3aSR,8RS,8aRS)-methyl 5,6-dimeth-oxy-3a,10-dimethyl-1-phenyl-3,3a,8,8a-tetra-hydro-3,8-(epimino-methano)-cyclo-penta-[a]indene-2-carboxyl-ate from synchrotron X-ray diffraction.

Abstract

The title compound, C25H27NO4 (I), the product of the unusual thermolysis of aza-cyclic allene methyl 10,11-dimeth-oxy-3,8-dimethyl-6-phenyl-3-aza-benzo[d]cyclo-deca-4,6,7-triene-5-carboxyl-ate, represents a bicyclic heterosystem and crystallizes in the monoclinic space group P21/c with three crystallographically independent mol-ecules in the unit cell. These independent mol-ecules adopt very similar geometries and differ only in the conformations of the two meth-oxy substituents on the benzene ring. In two of the three independent mol-ecules, both meth-oxy groups are almost coplanar with the benzene ring [the C-C-O-Me torsion angles are 10.8 (2), 12.3 (2), 9.1 (2) and 13.6 (3)°], whereas in the third mol-ecule, one of the meth-oxy groups is practically coplanar to and the other meth-oxy group is roughly perpendicular to the benzene ring, the C-C-O-Me torsion angles being 14.1 (2) and 76.5 (2)°. The mol-ecule of (I) comprises a fused tetra-cyclic system containing two five-membered rings (cyclo-pentenes) and two six-membered rings (piperidine and benzene). The five-membered rings have the usual envelope conformation, with the methyl-subsituted C atom as the flap in each molecule, and the six-membered piperidine ring has a chair conformation. The methyl substituent at the N atom occupies the sterically favourable equatorial position. The carboxyl-ate group lies almost within the basal plane of the parent cyclo-pentene ring [making dihedral angle of 11.68 (8), 18.94 (9) and 15.16 (9)° in the three independent mol-ecules], while the phenyl substituent is twisted by 48.26 (6), 42.04 (6) and 41.28 (6)° (for the three independent mol-ecules) relative to this plane. In the crystal, mol-ecules of (I) form stacks along the b-axis direction. The mol-ecules are arranged at van der Waals distances.