Cryptands methodology

The hrst opticaUy active macrobicycles and macropolycycles were repotted by Lehn and co-woricers (187) in 1974. Employing the synthetic methodology developed in Strasbourg for the preparation of cryptands, chiral molecular receptors, such as (5)-191 and (5)-192, have been isolated and characterized. 

Since the early years of its discovery (32), there have been a number of synthetic approaches made and a large number of cryptands are now reported in the literamre. The synthesis of these molecules has two aspects (1) methodology and (2) strategy, which are briefly discussed next. 

Recently the synthesis of the macrocyclic tetramine below (Scheme 3) was reported [5]. The encrypted nitrogens are very basic (pK, 24.9 in MeCN) and it was observed that chloroform is dehydrohalogenated in its presence to give dichlorocarbene. Because this new cryptand and related cage structures shown below (such as the diamine [6], the commercially available diamine triether [7] and the pentamine [8], Scheme 3) have thus far not experienced significant application in organic methodology, they will not be further treated herein. 

Due to cation complexation and aftereffects relating to the increased solubility of inorganic salts in low-polarity organic media and enhanced activity of the counterion reactant (quasi-naked anion), the podands, just as the crown compounds and cryptands, are promising catalysts in the synthetic methodology of phase-transfer catalysis. 

Several chiral crown ethers incorporating glycoside moieties have been reported. The [2.2.l]cryptand (8), with a 2,3-alkylated methyl 4,6-0 -C(S)-phenylethylidene]-a-D-mannopyranoside moiety (having an axial phenyl group) has been synthesized following previously employed methodology (V0I.17, p.S ). " Similarly,... 

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