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 (SNAr) reaction of lithium benzylamide with tetra-O-methylsulfinylcalix[4]arenes 4(rctt) and 4(rcct), respectively. The SNAr 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-tert-butylthiacalix[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.
Original language | English |
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Pages (from-to) | 9608-9616 |
Number of pages | 9 |
Journal | RSC Advances |
Volume | 4 |
Issue number | 19 |
DOIs | |
Publication status | Published - 2014 |
ASJC Scopus subject areas
- Chemistry(all)
- Chemical Engineering(all)