UNSATURATED HETEROCYCLIC SYSTEMS .55. CYCLOADDITION REACTIONS OF DERIVATIVES OF 1H-AZEPINE

The cycle additions of N-substituted azepines to various dienophiles and dienes have been studied. With tetracyanoethylene, the azepines add as 1,4-dienes without prior valence bond isomerization; however, a directional specificity is observed with the monomethyl ring substituted examples. With N-phenylmaleimide, there is again evidenced 1,4 addition to the seven-membered ring, the stereochemical outcome (endo) being in agreement with orbital symmetry considerations. In the case of isobenzofurans, (4 + 2)π cycloaddition to the 4,5 bond of the azepines occurs. Significantly, the stereochemistry of these reactions is likewise endo. 2,5-Dimethyl-3,4-diphenylcyclopentadienone functions in a similar fashion. Therefore, this kinetic preference for addition to the double bond of the azepine ring most remote from the nitrogen atom does not appear to be dependent on the electronic characteristics of the 4π donor. These results indicate that the 1H-azepine nucleus is unique in its capability to undergo thermally induced cycloaddition reactions without recourse to prior valence tautomerism. © 1969, American Chemical Society. All rights reserved.