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. 2021 Nov 3;9(Pt 1):43–48. doi: 10.1107/S2052252521010563

Table 1. Base-dependent synthesis of three regioisomers of singly bridged calix[6]crown-6.

Reaction conditions: calix[6]arene (1.0 equiv), base (2.0 equiv), penta­ethyl­ene glycol di­tosyl­ate (0.9 equiv), xylene (500 ml), reflux. Selectivity ratios were determined by 1H NMR.

  Selectivity ratio (%)  
Base H4 L 1,2 H4 L 1,3 H4 L 1,4 Total yield (%)
Na2CO3 75 15 10 32.4
K2CO3 49 43 8 33.6
Rb2CO3 17 22 61 32.5
Cs2CO3 0 17 83 35.9