Eight-membered Rings containing One Heteroatom

Details have been reported of formation of c/5-oxa- and -aza-a-bis-homo-benzenes (364) by heating (363), the reaction being reversible in the cases 

R2 = Me, X = Protons and appear in the aromatic region of the n.m.r. spectrum. Further work on transannular interactions in hepta-methyleneimine derivatives has indicated that (365) reacts as a transannular enamine as shown, and that the reduced basicity of the cyanomethyl substituted amine (366) allows ketal protonation to compete with JV-protonation so that treatment with acid gives the bicyclic derivative (367).  

A number of interesting papers on azocine ring synthesis have appeared. l-Methyl-l,4-dihydroquinoline reacts with DMADC to give the isolable cyclobutene adduct (368), which on heating affords the 1,6-dihydro-l-benzazocine ring (369), although comparable results could not be obtained 

Chabudzinski, D. Sedzik-Hibner, U. Lipnick and G. Piotrowska, Roczniki Chent., 1972, 46, 1089. 

Yamada, T. Konakahara, S. Ishihara, H. Kanamori, T. Itoh, K. Kimura, and 

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