S. S. Basok

Controlled self-assembly of bis(crown)stilbenes into unusual bis-sandwich complexes: structure and stereoselective [2+2] photocycloaddition

It was shown by 1H NMR spectroscopy that symmetrical bis(crown)stilbenes (L) and small alkali and alkaline-earth metal cations form 1(L) ∶ 1(Mm+) and 1(L) ∶ 2(Mm+) complexes in MeCN solutions. In the case of large or hydrated metal cations such as Cs+, Rb+, K+, Ba2+, Sr2+, [Ca(H2O)x]2+ and stilbenes with a small crown-ether cavity as compared with the metal cation size, stable bis-sandwich complexes 2(L) ∶ 2(Mm+) can also be formed. A stable bis-pseudosandwich 2 ∶ 2 complex is also produced from bis(18-crown-6)stilbene with the propanediammonium ion. The effect of the crown-ether size and the cation size and nature on the route of stilbene phototransformation and product composition was elucidated. The bis-(pseudo)sandwich complexes undergo effective stereoselective [2+2] photocycloaddition giving mainly rctt isomers of new 1,2,3,4-tetracrown cyclobutanes. The structures of complexes of bis(crown)stilbenes and obtained cyclobutanes were confirmed by X-ray diffraction.

Synthesis and structure of bis-crown-containing stilbenes

An improved procedure was proposed for the synthesis of stilbenes fused to two crown ether fragments at both benzene rings. The structure of new homologous symmetric bis-crown-containing stilbenes was determined by X-ray analysis. Relations were revealed between the size of the crown ether moiety and stilbene conformation in crystal and the mode of crystal packing. Conformational analysis of the prepared stilbenes in solution and in the solid state was performed by 1H and 13C NMR spectroscopy and by DFT quantum-chemical calculations.

Specific features of the reduction of disubstituted amide derivatives of p-tert -butylcalix[4]arene

Regardless of the reducing agent, the reduction at 25°C and higher of the amide groups in a large number of p-tert-butylcalix[4]arene derivatives containing amide fragments with different substituents on the nitrogen atoms was accompanied by hydrogenolysis of the C-N bond with formation of the corresponding O-(2-hydroxyethyl) calixarenes and by partial cleavage of the ether bond between the calixarene framework and the substituent to give compounds with a lower degree of substitution.

Host-guest complexes of nitro-substituted N-alkylbenzoaza-18-crowns-6

A number of N-alkyl(nitrobenzo)aza-18-crowns-6 in which the nitrogen atom in the macroring is conjugated with the benzene ring were synthesized, and their complexing power was compared with that of model nitro derivatives of benzo-18-crown-6 and N-phenylaza-18-crown-6 using 1H NMR spectroscopy and DFT/PBE quantum-chemical calculations. The stability constants of the complexes formed by crown ethers with NH4/+, EtNH3/+, Li+, Na+, and K+ in CD3CN were determined by 1H NMR titration. The complexing power of N-alkyl(nitrobenzo)aza-18-crowns-6 toward metal and ammonium cation was considerably higher than that of N-(4-nitrophenyl)aza-18-crown-6 and N-alkyl(nitrobenzo)aza-15-crown-5 and was comparable or higher than that of nitrobenzo-18-crown-6.

From chains to ladders in co-crystals with 2,3-thiophene-15-crown-5, 2,3-naphtho-15-crown-5, and bis-(18-crown-6)-stilbene constructed by weak hydrogen bonding

For the first time a series of co-crystals of 2,3-thiophene-15-crown-5 1, 2,3-naphtho-15-crown-5 2, bis-(18-crown-6)-stilbene 3 with dithiooxamide a, 1,2,5-oxadiazole-3,4-diamine b, and 3-nitro-1H-1,2,4-triazole c with compositions 1a, 2a, 2b·H22O, 2c, and 3a22 were prepared and their structures were studied by X-ray crystallography. The components in the co-crystals demonstrate the different modes of mutual arrangement and contribution of diverse weak interactions to the final architecture. Infinite chains of the alternating component molecules linked by N–H⋯O hydrogen bonds characterise the structures of 1a and 2a, whereas in the case of 3a22 formation of the loosely packed ladder-type structure was observed. In 2b·H22O the planar naphtho- and oxadiazole moieties demonstrate their edge-to-face arrangement, while in 2c the partially overlapping naphtho- and triazole moieties provide effective face-to-face π–π stacking interactions. The improved synthetic strategy for 1 and 2 is given.

Synthesis of crown-containing 2-styrylbenzothiazoles. Effect of alkali metal cations on the condensation of crown-ether benzaldehydes with 2-methylbenzothiazole

Methods for the synthesis of unknown 2-styrylbenzothiazoles containing crown ether moieties with different combinations of O, S, and N-heteroatoms based on the Wittig reaction or condensation of 2-methylbenzothiazole with crown-ether benzaldehydes in the presence of strong bases or acids are proposed. The condensation in the presence of bases is accompanied by complex formation with participation of the crown ether moiety of the benzaldehyde. The complex formation has a pronounced influence on the yield of the target product and the pattern of condensation of 2-methylbenzothiazole with crown-ether benzaldehydes.

p-tert-butylcalix[4]arenes containing azacrown ether substituents at the lower rim as potential polytopic receptors

A series of disubstituted p-tert-butylcalix[4]arenes with N-methoxycarbonylmonoazacrown ether and N-ethoxymonoazacrown ether residues at the lower rim has been prepared via the reaction of di(carboxymethoxy)-p-tert-butylcalix[4]arene with azacrown ethers and subsequent reduction of the resulting amide derivatives. Using UV titration and 1H NMR spectroscopy we have demonstrated the ability of the calixarene with two N-carbonylmonoaza-18-crown-6-ether substituents to form the 1:3 complexes with K+ and Na+ and the 1:2 complexes with Cs+, Sr2+, Cu2+, and Zn2+. The calixarene with two fragments of N-ethoxymonoazo-18-crown ether has formed binuclear complexes with alkali metals cations and mononuclear complexes with transition metals cations.

Synthesis of derivatives of p-tert-butylcalix[4]arene containing on lower rim fragments of 2-aminoalkylbenzimidazoles

Reactions of calix[4]arene carboxymethoxy derivatives with 2-aminoalkylbenzimidazoles in the presence of dicyclohexylcarbodiimide and hydroxybenzotriazole afforded a series of p-tert-butylcalix[4]arene derivatives containing on the lower rim N-(2-benzimidazolylalkyl)carbamoylmethoxy fragments. The reaction carried out in the absence of hydroxybenzOtriazole resulted in macrocycles containing one N-(2-benzimidazolylalkyl)carbamoyl fragment and a fragment of N-(acyl)dicyclohexylisourea.

Synthesis and Complex-Forming Properties of N-Substituted Diazacrown Ethers

N-Substituted mono- and diazacrown ether with ethoxycarbonylmethyl, 7-phenyl-3,6-dioxaheptyl, p-methoxy, and p-nitrobenzyl groups in the side chain have been synthesized. Their reactions with alkali and alkaline-earth metals have been studied. Substituents affect the complex-forming ability of the “base” macrocycle by changing the basicity of the nitrogen atoms and coordinating with the complexing ion.

Synthesis of monoazacrown ethers under phase-transfer catalysis

A procedure has been proposed for the synthesis of monoazacrown ethers by reaction of N-benzyldiethanolamine with oligo(ethylene glycol) bis-p-toluenesulfonates in a two-phase system aromatic hydrocarbon-50% aqueous alkali, followed by removal of the benzyl group by catalytic hydrogenolysis. The maximal yields of N-benzylaza-12-crown-4, -18-crown-6, and -21-crown-7 were achieved by adding 4–10 equiv of LiCl, BaBr2, and CsCl, respectively, to the reaction mixture, which probably indicated template effect.