Trans-diaryl epoxides:: Asymmetric synthesis, ring-opening, and absolute configuration

Anthryl-phenyl, phenanthryl-phenyl, and naphthyl-phenyl trans-epoxides (1, 2, and 3, respectively) having enantiomeric purities of 95%, 99%, and 96% were synthesized from a diastereo and enantiopure sulfonium salt derived from Eliel's oxathiane. The determination of their (1R,2R) absolute configurations was achieved by application of the CD exciton chirality method using a Zn-porphyrin tweezer on the corresponding alcohols obtained after opening of these epoxides with LiAlH4. The Rconfiguration at C2 of these epoxides, (-)-l, (+)-2, and (-)-3, is consistent with our previous results concerning asymmetric synthesis of monoaryl epoxides, cyclopropanes, and aziridines. The (1 S,2R) -configuration of the cis isomer (when present) was also confirmed. Moreover, the agreement between the negative exciton chirality for conjugates of (S) -configuration predicted by molecular modeling and the observed CD spectra helps to clarify the relative steric size of phenyl and CH2-aryl (phenanthryl or anthryl), which is critical when the tweezer method is applied for absolute configurational assignment (phenyl = medium group; anthacenyl CH2 and phenanthryl CH2 large group). Chirality 16:196-203, 2004. (C) 2004 Wiley-Liss, Inc.