the enaminones 4a–4e by the following two routes: (A): Acylation of the enamines, 2, derived from 1 and secondary amines (pyrrolidine, morpholine and piperidine) by ethyl chloroformate, and (B): Condensation of 1 with diethyl oxalate, giving the β-ketoesters 3, followed by reaction with the secondary amines. Ethyl 2(-1-pyrrolidinyl)-1-cyclopentene-1-carboxylate, 4f, and methyl 3-(1-pyrrolidinyl)-2-butenoate
and intermediates, which can be trapped under certain conditions, as well as previous investigations of single steps of the in situ reaction sequence involved in the carbocyclization are used to arrive at a tentative proposal for the stericcourse of these steps: (i) intermolecular coupling of the trigonal centers of enamine and nitroolefin with preferred relative topicity like, (ii) intramolecular coupling