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.