Stereochemical Peculiarities of the Products of Condensation of Piperidine-4-one with Aromatic Aldehydes

This paper presents the results of investigations on conformation peculiarities of the condensation products of piperidine-4-ones containing arylidene, hydroxyarylmethyl as well as both arylidene and hydroxyarylmethyl substituents. Synthesized α, β-unsaturated ketones can be used to investigate conformation of cycles fixing a conjugated system of carbonyl and double bonds. Synthesis of α, β-unsaturated piperidine-4-ones was carried out according to the reaction of Claisen-Schmidt by condensation of piperidine-4-ones with aromatic aldehydes. The reaction was carried out in methanol medium in the presence of an alkaline agent. High resolution 1H and 13C NMR resonance assignments and conformational assignments were carried out for four 3- arylidene or hydroxyarylmethyl and 3- arylidene-5- hydroxyarylmethyl substituted piperidine-4-ones (1-4). As a result of the initial aldol condensation of piperidine-4-ones with aromatic aldehydes an aryloxymethyl group in the intermediate compound can have both an equatorial and axial position. Conformation of a conjugated system proved to be electronically effected by the presence of nitrogen atom in the heterocycle. At the same time, conformation peculiarities of α, β-unsaturated ketones under study are developed at the stage of their synthesis. This is explained by the fact that in the course of the reaction there appears a new sp2 -centre, this resulting in our case in the change of the conformation of “a chair”. There takes place flattening of the structure and fixation of s-cis conformation. Furfurilidene substituent is conjugated with a carbonyl group, there forms a planar structure including 2, 3, 4 and 5 atoms of hydrogen of piperidine cycle and furfurilidene substituent and there exist two isomers with cis- (A) and trans- (B) position of a furyl ring at double bond in relation to a carbonyl group