THERMOCHEMICAL REACTIONS OF 1H-AZEPINE DERIVATIVES .I. DIMERIZATION

Heating of several 1-substituted 1H-azepines at 120-130° for short periods of time has been found to afford crystalline dimers. Classification of these dimerizations as (6 + 4) π cycloadditions was based upon ultimate degradation of the unsubstituted dimers to ethylcyclodecane. The stereochemistry of the dimerization was established as exo by X-ray crystallographic structure determination of a derived methiodide. It is suggested that the transition states of such reactions are controlled to a significant extent by orbital symmetry factors since the exo-bonding process is favored on the basis of secondary orbital interactions. Thermolysis of the monomeric 1H-azepines or their low-temperature dimers at 200° for several minutes was observed to give rise to different dimers. These high-temperature dimers were shown to be derivatives of the highly symmetrical 13,14-diazatricyclo[6.4.1. 12,7]-tetradeca-3,5,9,11-tetraene system. The mechanistic interrelationship of the two types of dim rs is discussed. © 1969, American Chemical Society. All rights reserved.