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

Abstract

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.