Crowned arborols

Shinkai et al/73,74 have reported the construction of crowned arborols that incorporated diaza crown ethers as spacers, and three-directional, aromatic branching centers (Scheme 5.24). In this case, the convergent construction was found to be more effective than the divergent approach. Tetraoxadiazacrown monomer 93 was prepared from N-benzyloxycarbonyldiazacrown ether (94) and a monoacyl chloride 95, affording the diprotected intermediate 96, which was catalytically debenzylated (Pd/C, H2) to give diester 93 or hydrolyzed (aq.base) to afford diacid 97. Monomer 97 was then transformed to tetraester 98, by means of the mixed anhydride method, with two equivalents of the... 

A related reduced series (Figure 5.5) was also reported J74 Selectivity of these crowned arborols (100-102) towards alkali metal cation binding was examined and allosteric as well as conformational binding effects were studied. Also they showed that the sterically less crowded arborols (e.g., 102) are better for the dissolution of myoglobin in organic solvents, such as DMF. This example affords an interesting entrance to internal metal ion complexation at a specific loci see Section 8.3. 

Scheme 5.24. Shinkai et al. s[731 procedure for the synthesis of crowned arborols ...

Figure 5.5. Reduction of the carbonyl moieties of the crowned arborols (Scheme 2.24) afforded these more lipophilic crowned dendrimers.

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