Synthesis and Conformational Studies of Regio- and Conformational Isomers Derived from O-Benzylation of Tetrahydroxy[3.1.3.1]metacyclophanes

✍ Scribed by Takehiko Yamato; Yoshiyuki Saruwatari; Masashi Yasumatsu; Seiji Ide

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 589 KB
• Volume: 1998
• Category: Article
• ISSN: 1434-193X
• DOI: 10.1002/(sici)1099-0690(199802)1998:2<309::aid-ejoc309>3.0.co;2-6

✦ Synopsis

Regioselective O-benzylations of [3.1.3.1]metacyclophanes lated product 2 in a ratio of 80:20 (cone-2/1,4-alternate-2) is obtained in 83% yield. Thus, the alkali metal cation plays with intraannular OH groups are described. O- Benzylation of 6,13,22,16,25,not only an important role with regard to the regioselectivity, but also in determining the number of O-benzylations that [3.1.3.1]metacyclophane 1 with 2 equiv. of benzyl bromide in the presence of Na 2 CO 3 leads to exclusive formation of the occur, as a consequence of the template effect. Regioselective syntheses of dimethoxy-and trimethoxy[3.1.3.1]meta-monosubstituted product 3. In contrast, use of K 2 CO 3 as the base leads to di-O-substitution, resulting in the disubstituted cyclophanes are accomplished by a protection-deprotection strategy, using the benzyl residues as protecting groups. The product, distal-4, as the major product, along with some 1,2proximal-4, in spite of using a large excess of benzyl bro-1 H-NMR spectra of these macrocyclic metacyclophanes are also discussed. mide. Under the same reaction conditions in the presence of Cs 2 CO 3 , a mixture of two conformers of the tetra-O-benzy-