Zur-Reaktionsweise von Enaminen mit Cyclopropenonen III. Isolierung eines Produktes der «C,C-Insertion»

From the reaction of the N-(2-Methylpropenyl)-pyrrolidin 6 with diphenylcyclopropenone 7 we isolated as a byproduct 5-Methyl-2, 4-diphenyl-1-pyrrolidino-hexa-1, 4-diene-3-one 9 . The structure was proven by an interpretation of the IR.-, NMR.- and MS.-spectra. This result is of importance since it represents the first case of a direct ‘C, C-insertion’ product 4 from the reaction of an enamine 1 and a cyclopropenone 2 and because structures of type 4 (including 9 ) have previously been postulated for the main products of this reaction, which were later shown to be amides 3 (including 8 ). Acid hydrolysis of the β-amino-dienone 9 yielded the dihydropyrone 10 and the cyclopentenone 11 . These isomeric products are considered to be the result of two electrocyclic reactions, one of a hexa-2,4-diene-al 12 and the other of a hexadienylium ion 14 .