Additionsreaktionen von 2‐Amino‐1‐azetinen mit Cyclopropenonen; Bildung von Azepinderivaten durch Ringerweiterung. Vorläufige Mitteilung

Addition Reactions of 2‐Amino‐1‐azetines with Cyclopropenones; Formation of Azepine Derivatives by Ring Expansion Reactions The reaction of 2‐amino‐1‐azetines of type 6 with 2,3‐diphenylcyclopropenone ( 1a ) in acetonitrile leads to azetol[1,2‐α]pyrroles ( cf. 7 and 9 , Schemes 3 and 4 ) in good yield. It is remarkable that in the reaction of 6a with 1a only endo ‐ 7 is formed. With silicagel in ether endo ‐ 7 isomerizes to the thermodynamically more stable exo ‐ 7 ( Schemes 3 and 6 ). The crystal structure of the latter compound has been established by X‐ray crystallography. The reaction of 6a and 2‐isopropyl‐3‐phenyl‐cyclopropenone ( 1b ) yields only one product, which isomerizes with silicagel in ether to exo ‐ 10 ( Scheme 4 ). The structure of exo ‐ 10 has been determined by NMR‐spectroscopy. It seems reasonable that this structure results from a nucleophilic attack of the four‐membered amidine to the phenyl‐substituted C‐atom of 1b.