Investigations into the reactions of enamines and imines.

Abstract

The alkylation of 2-methylcyclohexanone imines using methyl acrylate has been investigated with a view to optimising the reaction conditions. The mechanism of this alkylation reaction has been investigated and it has been shown that the alkylation does not proceed via a 2,6-intermediate which subsequently undergoes a rearrangement to the 2,2-product, but rather proceeds directly to the 2,2-product. As it had been shown that the alkylation of 2-substituted cyclohexanone imines in dry methanol occurred at the more substituted position, it was decided, in the light of certain apparently anomolous patent work, to investigate the alkylation of unsubstituted cyclohexanone imines using a variety of electrophilic alkenes. The results show that in certain instances, 2,2-bis-alkylation occurs and in others, mono-alkylation and that it is the strength of the electron-withdrawing group attached to the alkene which determines whether 2,2-bis-alkylation occurs or not. The reasons for this are discussed in the text. The preparation of a number of novel 2,2-bis-eyclohexanones and an octahydroquinoline are described. The reaction of I-phenyl-2-propen-l-one (phenyl vinyl ketone) with the benzylaluine imines of 2-butanone and I-phenyl-2-propanone in methanol gave gave two novel bicyclic diones, whereas the reaction between the benzylamine imine of 3-pentanone with I-phenyl-2-propen-l-one gave only mono-eyclic products only even though there appeared to be no impediment to the formation of the bicyclic compound. The structures were determined using nuclear magnetic resonance and confirmed by X-ray crystallography. The reaction between I-phenyl-2-propen-l-one and N-(l-phenyl-l-ethylidene)benzylamine gave after hydrolysis only the mono-substituted product, 1,5-diphenyl-l ,5-pentandione.