A joint experimental and theoretical structural study of novel substituted 2,5-dioxo-1,2,3,4,5,6,7,8-octahydroquinolines

A series of substituted 2,5-dioxo-1,2,3,4,5,5,7,8-octahydroquinolines have been synthesised from Meldrum's acid and dimedone in the presence of different aldehydes by following an approach similar to the one developed by Hantzch. The structure of these compounds has been thoroughly studied by X-ray crystallographic analysis and semiempirical (AM1) and ab initio (HF/3-21G) methods, and two favoured conformations are possible. A good agreement is found between the theoretical and experimental values. The most stable conformation (A) in the solid state is also that favoured in solution, according to the proton coupling constant determined from Karplus' and Altona's equations and H-1 NMR spectroscopic experiments. (C) 1998 Elsevier Science Ltd. All rights reserved.