Penta-substituted arene

Paulsen, H., Antons, S., Brandes, A., et al. (1999) Stereoselective Mukaiyama-Michael/Michael/Aldol domino cyclization as the key step in the synthesis of penta-substituted arenes an efficient access to highly active inhibitors of cholesteryl ester transfer protein (CETP). Angew. Chem. Int. Ed. 38, 3373-3375. 

SCHEME 4 Synthesis of the penta-substituted arene subunit of psymberin. 

In cooperation with the group of Dirk Volkmer (Ulm University), the synthetic procedure established for the preparation of the tetra-(4-(2,2 6, 2"-terpyridyl)-phenyl)-cavitand 49 was adapted for the synthesis of terpyridyl-substituted calix [n]arenes [77]. The tetra-(4-(2,2 6, 2"-terpyridyl)-phenyl) calix[4]arenes 54a,b and the penta-(4-(2, 2 6, 2"-terpyridyl)-phenyl)calix[5]arene 55 can be prepared from the boronic acid ester 48 and tetrabromocalix[4]arene 52a or b and pentabromocalix[5]arene 53, respectively (Fig. 21). 

Due to the increased number of OH functionalities, 29 pyridino homologues of p-tert-butylcalix[8]arene 21 can exist one mono-, hepta-, and octa-substituted derivatives, four di-, five tri-, eight tetra-, five penta- and four hexasubstituted regioisomers. The products of the peutial alkylation of 21 with PicCl-HCl are hitherto unknown, while fully alkylated octakis[(2-pyridylmethyl)oxy]calix[8]arene 22 has been obtained in 24% yield by using conditions similar to those described for calix[6]arene 20. From solvent extraction data, Shinkai has shown that compounds 20 and 22 display a high affinity for UO " at elevated temperature (100°C, o-dichlorobenzene) [26]. 

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