Unusual thermolysis of azacyclic allene under microwave conditions: crystal structure of (3RS,3aSR,8RS,8aRS)-methyl 5,6-dimethoxy-3a,10-dimethyl-1-phenyl-3,3a,8,8a-tetrahydro-3,8-(epiminomethano)cyclopenta[a]indene-2-carboxylate from synchrotron X-ray diffraction

Abstract

The title compound, C25H27NO4 (I), the product of the unusual thermolysis of azacyclic allene methyl 10,11-dimethoxy-3,8-dimethyl-6-phenyl-3-azabenzo[d]cyclodeca-4,6,7-triene-5-carboxylate, represents a bicyclic heterosystem and crystallizes in the monoclinic space group P21/c with three crystallographically independent molecules in the unit cell. These independent molecules adopt very similar geometries and differ only in the conformations of the two methoxy substituents on the benzene ring. In two of the three independent molecules, both methoxy 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 molecule, one of the methoxy groups is practically coplanar to and the other methoxy group is roughly perpendicular to the benzene ring, the C—C—O—Me torsion angles being 14.1 (2) and 76.5 (2)°. The molecule of (I) comprises a fused tetracyclic system containing two five-membered rings (cyclopentenes) 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 carboxylate group lies almost within the basal plane of the parent cyclopentene ring [making dihedral angle of 11.68 (8), 18.94 (9) and 15.16 (9)° in the three independent molecules], while the phenyl substituent is twisted by 48.26 (6), 42.04 (6) and 41.28 (6)° (for the three independent molecules) relative to this plane. In the crystal, molecules of (I) form stacks along the b-axis direction. The molecules are arranged at van der Waals distances.

Keywords

• crystal structure
• azacyclic allenes
• thermolysis
• microwave synthesis
• (epiminomethano)cyclopenta[a]indene
• 3-benzazepine
• synchrotron X-ray diffraction