Regioselective synthesis of 1,2- and 1,3-diaminothiacalix[4]arenes via nucleophilic aromatic substitution and their X-ray structures

Abstract

Thiacalix [4]arenes bearing two amino groups instead of two hydroxy groups of p-tert-butylthiacalix[4]arene(2) at the distal 1,3-(5b) and proximal 1,2-positions (5c) are regioselectively synthesized via the nucleophilic aromatic substitution (S N Ar) reaction of lithium benzylamide with tetra-O-methylsulfinylcalix[4]arenes 4(rctt) and 4(rcct), respectively. The S N Ar reaction selectively proceeds at the benzene rings between two neighboring sulfinyl groups of a trans conformation. This is rationalized by the cooperative coordination of a methoxy group with a neighboring sulfinyl oxygen atom toward the metal ion to form a six-membered chelate, through which the amide ion attacks the aromatic nucleus. The N,O-hybrid thiacalixarenes 5b and 5c adopt cone conformations in their acetonitrile inclusion crystals. The distances between adjacent N and/or O atoms of their narrow-rim substituents indicate that the four substituents form a circular hydrogen-bond network but it is weaker than that of original thiacalixarene 2. Compound 5c also adopts a cone conformation in the guest-free crystal. This, combined with the fact that tetraaminated p-tertbutylthiacalix[4]arene 5a adopts a 1,3-alternate conformation in its guest-free crystal, indicates that the intramolecular O/N hydrogen bonds, not to mention the O/O hydrogen bond, in compound 5c play a crucial role in maintaining a cone conformation in the crystal.

Promising advances of thiacalix[4]arene in crystal structures

“…Thiacalix [4]arene analogues 9 and 10 ( Fig. 6), 26 with two amino groups at the lower rim, are also in a cone conformation with a circular H-bonded array in their crystals ( Fig. 9a and b).…”

Synthesis and Characterization of a Novel Bis‐Sulfoxide and Its Evaluation as a Ligand in p‐Block Chemistry

“…For example, the bis-sulfoxide derivatives are used as ligands in the stabilisation of transition metal or lanthanide complexes or as ligand in transition metal-catalyzed reactions or in various catalytic processes. [5,7,[9][10][11][12][13][14][15][16][17][18] In most of the cases the coordination to the metal center is realized through the sulfur atom of the sulfinyl group, [5,11,14,15,[18][19][20][21][22][23] however, coordination through the oxygen atom is also a possibility, some examples are presented in the literature. [12,14,[23][24][25][26] The synthesis of the sulfoxides can be realized by different methods such as the arylation of sulfenate anions by a coupling reaction, a nucleophilic substitution or an electrophilic attack, with the formation of a C-SO bond, [27][28][29][30][31] or by oxidation of a sulfide through a thioether as intermediary derivative.…”

“…Derivatives containing two sulfinyl groups with different roles, in the chemical processes are also known. For example, the bis‐sulfoxide derivatives are used as ligands in the stabilisation of transition metal or lanthanide complexes or as ligand in transition metal‐catalyzed reactions or in various catalytic processes , , . In most of the cases the coordination to the metal center is realized through the sulfur atom of the sulfinyl group,, , , , however, coordination through the oxygen atom is also a possibility, some examples are presented in the literature , , …”

1,3-Diiodocalix[4]arene: Synthesis by Ullmann-Type Iodination of 1,3-Bistriflate Ester of Calix[4]arene, Conformational Analysis, and Transformation into 1,3-Dicarboxy-, Diformyl-, and Dialkylcalix[4]arenes

“…Calixarenes (e.g., 1a ) and thiacalixarenes (e.g., 1b ), which are cyclic oligomers of phenols bridged at the ortho–ortho positions by methylene and epithio groups, respectively, are one of the most important building blocks in supramolecular chemistry. , A number of derivatives have been prepared via etherification or esterification of the hydroxy groups and/or electrophilic aromatic substitutions at the positions para to the hydroxy groups. However, displacement of the hydroxy groups with other functional groups by cleaving the aryl–oxygen bonds is difficult, because of steric hindrance caused by the sterically crowded cyclic structure and the presence of coordinative functional groups . Although C–O bond cleavage in aryl triflates using a palladium or nickel catalyst is one of the most reliable methods of replacing phenolic hydroxy groups, such reactions have been unsuccessful in the case of calixarenes, with the exception of the Sonogashira coupling of 1,3-bistriflate ester 2a , reported by Georghiou and co-workers .…”