Cation control on the synthesis of p-t-butylthiacalix[4](bis)crown ethers

Abstract

Abstract-Bridging of p-t-butylthiacalix[4]areneUnsubstituted thiacalix [4]arene is able to complex various transition metals, due to the presence of the bridging sulfur atoms. 7 The participation of sulfur in the complexation has been observed in X-ray crystal structures of complexes with alkali metal cations. 8 The complexation properties of thiacalix[4]arenes can be altered, both by functionalizing the lower rim with ligating sites or by oxidation of the bridging sulfur atoms. With 4 equiv. of Cs 2 CO 3 after 6 h, reaction of 1 with 2 (1.8 equiv.) exclusively afforded the 1,2-alternate thiacalix[4]biscrown-4 4 in 72% yield upon precipitation of the crude reaction mixture with methanol/acetone. Also the reaction of 1 and 3 (1.8 equiv.) with 4 equiv. of base gave a fast reaction (12 h, 100% conversion). The reaction gave a mixture of the 1,2-alternate thiacalix[4]biscrown-5 5 and the corresponding 1,3-alternate isomer 6. The pure thiacalix[4]biscrown-5 isomers 5 (27%) and 6 (15%) were isolated by fractional precipitation from methanol/acetone mixtures. Surprisingly, the proximal thiacalix[4]biscrowns-4 and -5 were only obtained in the 1,2-alternate conformation. The corresponding proximally substituted thiacalix[4]monocrown and proximally substituted cone thiacalix[4]biscrown compounds could not be detected. Compounds 4 and 5 were characterized by NMR ( 1 H and 13 C) and MS. 20,21 Definite proof for the 1,2-alternate thiacalix[4]biscrown-5 5 was obtained by an X-ray crystal structure (Fig. 1).22

Synthesis of Doubly Azacrowned Thiacalixarenes

“…Besides, all the patterns for tert-butyl, -CH 2 CO-and phenyl protons of 2a show good comparability to the 1,2:3,4doubly crowned calix[4]arene 5a which is in conic conformation. The patterns for tert-butyl and phenyl protons of 2b are also similar to those of 1,3-alternate thiacalix [4]arene-biscrowns-4,-5, and -6 which synthesised by reacting thiacalix [4]arene with tri-, tetra-, and pentaethylene glycol ditosylates [12][13][14] .…”

Switching Ion Binding Selectivity of Thiacalix[4]arene Monocrowns at Liquid–Liquid and 2D-Confined Interfaces

“…Previously reported results of extraction of thiacalixcrowns 2b and 6b , c [ 13 , 33 ] cannot be compared due to different organic phase and component ratio. Thus, liquid-phase extraction of alkali metal and Ag picrates by type I–III ligands was carried out ( Figure 4 a).…”

Synthesis, Structure, and Exctraction Ability of Tetrasubstituted Thiacalix[4]Arenes with Crown Ether Fragments on the Lower Rim

“…However, in the case of thiacalix [4]arenes, on the first step the formation of some by-products was observed, namely, products of 1,2-macrocyclization (Scheme 1, b), biscalixarenes [22] (Scheme 1, с), and biscrown-ether derivatives in 1,3-and 1,2-alternate conformations [23] (Scheme 1, d, e) and the target product can be obtained in rather low yield (Scheme 1, g). Other approach represents the primary synthesis of distal disubstituted thiacalixarenes (Scheme 1, f) with further crosslinking of remaining free hydroxyl groups by oligoethylene glycols.…”