Crystal structure of (1RS,21SR,22RS,24SR)-28-oxo-24-propyl-8,11,14-trioxa-24,27-diazapentacyclo[19.5.1.122,26.02,7.015,20]octacosa-2,4,6,15(20),16,18-hexaene acetic acid monosolvate

The crystal structure of a product of the Petrenko–Kritchenko condensation of N-propylpiperidone with 1,5-bis(2-formylphenoxy)-3-oxapentane and ammonium acetate was studied by X-ray diffraction

In attempts to apply this chemistry to obtain a macrocyclic ligand containing the N-propylsubstituted bispidine moiety, we studied the Petrenko-Kritchenko condensation of N-propylpiperidinone with 1,5-bis(2-formylphenoxy)-3-oxapentane and ammonium acetate. The reaction proceeded smoothly to give the expected azacrown system with a high yield of 73% (Fig. 1).
The prepared compound was studied by X-ray diffraction analysis. It is a stable complex and crystallized as an acetic acid monosolvate, C 26 H 32 N 2 O 4 (M)ÁC 2 H 4 O 2 , (I) (Fig. 2). This finding seems to show the possibility of forming the second piperidine ring by the direct participation of the ammonium ion without the loss of its counter-ionic nature.

Figure 3
The centrosymmetric hydrogen-bonded dimer of (I propyl substituent at the nitrogen atom N27 occupies the more favourable equatorial position. The molecule of M possesses four asymmetric centers at the C1, C21, C22 and C24 carbon atoms and can have potentially numerous diastereomers. The crystal of (I) is racemic and consists of enantiomeric pairs of M with the following relative configuration of the centers: rac-1R*, 21S*,22R*,24S*.

Supramolecular features
In the crystal, the hydrogen-bonded complex (I) forms centrosymmetric dimers by C-HÁ Á ÁO hydrogen bonds ( Fig. 3 and Table 1). The dimers interact through weak C-HÁ Á ÁO hydrogen bonds, forming layers parallel to ac plane ( Fig. 4 and Table 1).

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 2. The hydrogen atoms of the amino and hydroxy groups were localized in the difference-Fourier maps and included in the refinement with fixed positional (using a riding model) and isotropic displacement parameters [U iso (H) = 1.2U eq (N) and 1.5U eq (O)]. The other hydrogen atoms were placed in calculated positions with C-H = 0.95-1.00 Å and refined in the riding model with fixed isotropic displacement parameters [U iso (H) = 1.5U eq (C) for the methyl group and 1.2U eq (C) for the other groups].