Synthesis, crystal structure and conformational analysis of an unexpected [1,5]dithiocine product of aminopyridine and thiovanillin

Abstract

The condensation reaction of 2‐mercapto‐3‐methoxybenzaldehyde with 3‐aminopyridine afforded an unexpected N‐alkylated [1,5]dithiocine instead of the N‐salicylideneaniline. The proposed mechanism for this condensation involves a strong intramolecular hydrogen bond between the thiol and the amine groups, leading to a second condensation. The corresponding product, i.e. 4,10‐dimethoxy‐13‐(pyridin‐3‐yl)‐6H,12H‐6,12‐epiminodibenzo[b,f][1,5]dithiocine methanol 0.463‐solvate, C21H18N2O2S2·0.463CH3OH, was characterized by single‐crystal X‐ray diffraction analysis. The supramolecular structure shows π–π stacking and S…S interactions in the crystal packing. Within the asymmetric unit, two geometries of the N atom are observed. Although a planar geometry should be expected, a pyramidal one is observed due to the crystal packing. The presence of the two geometries was further supported by density functional theory (DFT) calculations that show an electronic energy difference of less than 2 kJ mol−1 between the two conformers.

Reactions of cobalt(ii) chloride and cobalt(ii) acetate with hemisalen-type ligands: ligand transformation, oxidation of cobalt and complex formation. Preliminary study on the cytotoxicity of Co(ii) and Co(iii) hemisalen complexes

“…Interestingly, the imine derivative of thiovanillin seems more prone to similar reaction of condensation since a cyclic compound very similar to C1A was obtained with a good yield in a non-catalyzed reaction between a thiovanillin and 3-AP conducted for one hour in dry, boiling ethanol. 31…”

“…Another likely mechanism of C1A formation, which includes the reaction between HL1 and o -vanillin generated as a result of partial hydrolysis of HL1 , is illustrated in Scheme 1S in ESI† (as in ref. 31).…”

“…Such reactions were catalyzed either with b-naphthol and a benzoquinone derivative, 40 with concentrated sulfuric(VI) acid, 41 or proceeded without the addition of a catalyst at the increased temperature (boiling ethanol). 31 Another example of acid-catalyzed cyclization has been published very recently. 32 Concerning the results described in the literature, we tested whether the dissolution of the HL1 ligand in acetonitrile would lead to the non-catalyzed self-cyclization in a time-frame reasonable for a chemist.…”

“…Interestingly, the imine derivative of thiovanillin seems more prone to similar reaction of condensation since a cyclic compound very similar to C1A was obtained with a good yield in a non-catalyzed reaction between a thiovanillin and 3-AP conducted for one hour in dry, boiling ethanol. 31 The possible mechanism of the self-cyclization reaction is presented in Scheme 3. Considering the probable formation of an intramolecular hydrogen bond between the imine bond N atom and hydroxyl group of HL1, the electrophilicity of imine carbon is increased.…”

“…[12][13][14][15][16][17] Schiff bases feature exciting properties related to the simultaneous presence of proton-donor and proton-acceptor groups, the possibility of formation of inter-and intramolecular hydrogen bonds and participation in proton transfer processes. [16][17][18][19][20][21][22][23][24] Based on these properties, imines are widely used in organic processes, such as the addition of organometallic reagents to C]N bond, 16,20,21,25,26 hydrolysis to aldehyde/ketone and amine, 21,27,28 self-condensation, 25,[29][30][31][32] complexation reactions with both main groups and transition metals, 21,33,34 pHand metal ion-dependent hydrolysis on the metal center during the formation of the coordination complex. [35][36][37][38] In our previous work, we described the immediate hydrolysis of the imine HL1 (2-methoxy-6-(E-2-pyridyliminomethyl)phenol) in the presence of nickel cations.…”