Heterocyclic dialdehydes: linkers in the synthesis of macroacyclic ligands

Abstract

Macroacyclic heteroatomic podands containing one chelation cavity were obtained as a result of the biscondensation of diethyl 2- [(2-aminophenyl)aminomethylidene]malonate with heterocyclic dialdehydes (2,5-thiophenedicarbaldehyde and 2,6-pyridinedicarbaldehyde).The synthesis of polydentate ligands is one of the urgent tasks of contemporary coordination chemistry [1][2][3]. By the inclusion of various heteroatoms, among them those forming part of heterocyclic fragments, in the chelate unit it is possible to vary the electronic and steric characteristics of the complexes precisely [4,5].In this work a path to the construction of new podands based on heterocyclic dialdehydes 2 and diethyl 2-[(2-aminophenyl)aminomethylidene]malonate (1) is presented. 2,5-Thiophenedicarbaldehyde (2a) and 2,6-pyridinedicarbaldehyde (2b) were used as heterocyclic dialdehydes.The diester 1 was obtained as a result of the monocondensation of o-phenylenediamine with diethyl 2-ethoxymethylenemalonate applying the procedure used for the synthesis of ethyl 2-[(2-aminophenyl)aminomethylene]-3-oxopropionates [6,7].We found that the diester 1 condenses regioselectively with the dialdehydes at the ethoxyl substituent forming the biscondensation products bisazomethines 3a,b. In the case of 2,5-thiophenedicarbaldehyde (2a) the reaction was conducted in benzene with azeotropic distillation of the water, and glacial acetic acid was used as catalyst. The condensation of the ester 1 with 2,6-pyridinedicarbaldehyde (2b) was conducted by boiling in absolute ethanol.The obtained compounds 3a,b can be subjects to imine-enamine tautomerism, and for this reason they can exist in the form of imine and/or enamine tautomers.The structure of compound 3a in the solid form was investigated by X-ray crystallographic analysis (Tables 1-3). It was found that the podand 3a in the crystal exists in the form of the s-cis,s-trans conformer of _______________ Dedicated to Academician V. N. Charushin on his 60th birthday

Crystal structures of four chiral imine-substituted thiophene derivatives

“…A systematic trend is thus emerging for these 2,5-substituted thiophenes, related to the potential twofold molecular symmetry: they have a strong tendency to crystallize in space groups that include at least one C 2 axis, such as C2 and P2 1 2 1 2 for the chiral crystals. This trend extends to achiral molecules, which also have twofold crystallographic symmetry in the space group C2/c (Kudyakova et al, 2011;Suganya et al, 2014;Boyle et al, 2015;Moussallem et al, 2015). The features shared by these related compounds could also be a signature of a propensity towards polymorphism between monoclinic and orthorhombic systems.…”

“…Many thiophenes substituted in the 2 and 5 positions by imine groups have been characterized; however, almost all were achiral compounds. X-ray structures have been reported mostly in space group C2/c (Suganya et al, 2014;Kudyakova et al, 2011Kudyakova et al, , 2012Bolduc et al, 2013b). Other represented space groups for achiral molecules are P2 1 (Skene & Dufresne, 2006) and P2 1 /c (Wiedermann et al, 2005).…”

2,5-Bis{[(–)-(S)-1-(4-methylphenyl)ethyl]iminomethyl}thiophene

“…For the structure of a chiral bis-aldimine compound, see: Espinosa Leija et al (2009). For structures of thiophenes substituted in positions 2 and 5 by imine functionalities, see: Skene & Dufresne (2006); Fridman & Kaftory (2007); de Lima et al (2010); Kudyakova et al (2011Kudyakova et al ( , 2012.…”

“…Other thiophenes substituted in positions 2 and 5 by imine groups have been characterized (e.g. Skene & Dufresne, 2006;Fridman & Kaftory, 2007;de Lima et al, 2010;Kudyakova et al, 2011Kudyakova et al, , 2012. However, all were achiral compounds, and only one actually presented a crystallographic C 2 symmetry (space group C2/c, Kudyakova et al, 2011), as in the title compound.…”