SYNTHESIS AND CONFORMATIONAL STUDIES OF SYN-DIHYDROXY[N.2]METACYCLOPHANES AND ANTI-DIHYDROXY[N.2]METACYCLOPHANES

syn- and anti-Dimethoxy[n.2]metacyclophanes 9 are obtained by pyrolysis of the corresponding anti-sulfones 8, which are prepared by the reaction of 1,n-bis[3-(chloromethyl)-2-methoxyphenyl]alkanes 6 with Na2S in ethanol under the high dilution conditions, followed by the oxidation of the obtained thiametacyclophanes 7 with m-chloroperbenzoic acid. Demethylation of anti-dimethoxy[n.2]metacyclophanes anti-9 with BBr3 in dichloromethane affords the corresponding anti-dihydroxy[n.2]metacyclophanes anti-10. On the other hand, demethylation of syn-dimethoxy[3.2]-syn-9b and -[4.2]metacyclophane syn-gc gives syn-dihydroxy[n.2]metacyclophanes syn-10b, c, but syn-dimethoxy[5.2]-syn-9d and -16.2]metacyclophane syn-9c are converted into the corresponding anti-dihydroxy[n.2]metacyclophanes anti-10d, e. AlCl3 . CH3NO2-catalyzed de-tert-butylation of tert-butyl-syn- and -anti-dihydroxy[3.2]- and -[4.2]metacyclophanes syn/anti-10b, c has been carried out in benzene to give the desired metacyclophanes anti-11a-c and syn-11c except syn-dihydroxy-[3.2]methacyclophane syn-11b which is converted into 8,17-epoxy[3.2]metacyclophane 13. The assignment of syn and anti conformations has been confirmed by H-1-NMR and lyses and X-ray diffraction studies. The dynamics of the ring inversion and UV spectra are also discussed.