Regioselective O-Substitution of p-tert-Butylcalix[7]arene

Abstract

[structure: see text]. The first examples of selectively functionalized calix[7]arenes have been obtained by weak-base promoted O-alkylation or O-benzoylation of p-tert-butylcalix[7]arene. Mono-, 1,3- and 1,4-disubstituted calix[7]arenes have been obtained in workable yields, while the 1,2,4,6-tetrasubstitution was achieved with surprisingly high selectivity (50-88% yield) by using K2CO3 as base. A rationale for this finding is proposed.

Conformational Features and Recognition Properties of a Conformationally Blocked Calix[7]arene Derivative

“…[10] Interestingly, with respect to the original 28-membered ring of parent 1, the trimeric 3/4-cone-like sub-ring of 2 is scaled down to a 24-membered ring. In similar previous work, [20] it was shown that the conformational rigidification of a 23-membered sub-ring of a 1,5-tetramethylene-bridged calix [8]arene derivative was possible by curtailing the oxygen-through-the-annulus route when sufficiently bulky groups were appended at the lower rim of the calix [8]arene macrocycle.…”

“…The first, obvious criterion followed to select compatible conformers was to discard those arrangements that lacked [8]. [23] closure of the calix [7]arene macrocycle.…”

“…f calcd [8] Table 1 on the calix [7]arene skeleton of 3. b) Lowest MM3 energy conformation 3 b (MacroModel 9.0, CHCl 3 GB/SA implicit model solvent) obtained from 3 a. c) Superimposition (rmsd = 0.96 ) of 3 a (light gray) and the X-ray structure (dark gray) of 4. d) Superimposition (rmsd = 0.86 ) of 3 a (white) and 3 b (black). tert-Butyl groups and substituents at the lower rim are omitted for clarity.…”

“…In fact, concerning chemical modification, we reported a procedure to achieve the 1,2,4,6-tetra-O-substitution of p-tert-butylcalix [7]arene 1 (Scheme 1) with high selectivity. [8] Successively, the first examples of 1,4-singly [9] and 1,4:2,3-doubly [10] bridged calix [7]arenes were obtained in yields of up to 72 and 76 %, respectively. More recently, examples of monosubstituted, [11] singly diacetylamido-bridged, [11] and multiply diphosphatebridged [12] calix [7]arenes were reported by Chen and coworkers.…”

Lower-Rim Substituted Calixarenes and Their Applications

“…The first example of selectively functionalized calix[7]arenes has been obtained by weak-base promoted O-alkylation or O-benzoylation of p -tert-butylcalix[7]arene. Mono, 1,3- and 1,4-disubstituted calix[7]arenes have been obtained in workable yields, while the 1,2,4,6-tetra substitution was achieved with surprisingly high selectivity by 50–88% yield by using pottassium carbonate as the base [40] (Figure 13). …”