Singly Bridged Calix[8]crowns

Abstract

Crowned calix[8]arenes are obtained by direct alkylation of p-tert-butylcalix[8]arene (1) with poly(ethylene glycol) ditosylates in the presence of various bases. K2CO3 promotes the preferential formation of 1,3-calix[8]crowns. Cs2CO3 mainly gives the 1,5-isomers, which are selectively obtained in high yields when shorter chains are used (1,5-crown-2, 88%; 1,5-crown-3, 78%). NaH affords the 1,4-isomers in yields up to 46%, often as the sole crown derivative, besides unreacted 1. 1,2-Calix[8]crowns are also obtained in appreciable amount in some instances. The observed regioselectivity is rationalized in terms of preferential formation of specific anions in dependence of the base strength. Dynamic NMR and modeling studies prove that the polyether chain, depending on its bridging mode, may significantly reduce the available space for the through the annulus passages leading to derivatives conformationally blocked (on the NMR time scale).

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

“…To overcome this kind of problem, we decided to resort to intramolecular bridging as a very convenient method to shape and preorganize larger calixarene macrocycles. [17,18] Thus, we focused our attention on doubly bridged calix [7]arene derivatives, [10] such as 2 (Scheme 1), in which the presence of two short bridges at the 1,4-and 2,3-positions led to a high level of preorganization and suggested potential applications as molecular hosts in supramolecular chemistry. The 1,4-bridging gives rise to two different tetra-and trimeric subunits in 2 defined by the four alkylated and the three unalkylated phenol rings, respectively.…”

Large Calixarenes: Synthesis and Properties

“…32 In fact, regarding the aromatic bridging elements, Neri and coworkers 33 in 2002 reported that the treatment of calix[8]arene 1e with Cs 2 CO 3 as base and aromatic shorts bridges such as ortho-, meta-, or para-bis(bromomethyl)benzene afforded to the 1,5-bridged calix[8]arene derivatives 11d-f ( Figure 10) in high yields (80-90%). Interestingly, the regioselectivity of the bridging reaction of the calix[8]arene macrocycle can be controlled by the reaction conditions and in particular by the base used and by the length and nature of the bridge.…”

Diamide Bridged Calix[8]arenes

“…Cs 2 CO 3 and NaH are generally used in the synthesis of 1,5-isomer. [4][5][6]17 However, using these bases in the reaction, either calix [8]arene remains unchanged or the products are too complex to be separated. Increasing of K 2 CO 3 to 8 equivalents has no remarkable effect on the distribution of products.…”

“…12 Amidebridged calixarenes can be reduced to calixazacrowns by LiAlH 4 . 13 Recently, we have synthesized a 1,3-diamide bridged calix[6]arene and an asymmetrical 1,3:4,5-doubly bridged derivative by reacting p-tert-butylcalix [6]arene with N,N¢-bis(chloroacetyl)ethylenediamine. 14 As an extension of the above work and to prepare calix[8]azacrown, the reaction of such a reagent and its homologue, N, N¢-bis(chloroacetyl)propylenediamine with p-tert-butylcalix[8]arene was investigated, and 1,5-diamide bridged p-tert-butylcalix [8]arenes and a 1,3:5,7-doubly diamide bridged p-tert-butylcalix[8]arene were obtained.…”

“…4 Direct alkylation of p-tert-butylcalix [8]arene with oligoethylene glycol ditosylates gave calix [8]crowns-n, and the bridging pattern depended on the nature of the base used. 5,6 Using oligoethylene glycol bischloroacetates in place of oligoethylene glycol ditosylates, a series of ester-containing 1,2-bridged calix [8]crowns have been obtained in reasonable yields. 7 Other diester bridged p-tert-butylcalix [8]arenes were obtained from p-tert-butylcalix [8]arene by reacting with adipoyl chloride in the presence of NaH.…”