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 R‐configuration at C2 of these epoxides, (–)‐1, (+)‐2, and (–)‐3, is consistent with our previous results concerning asymmetric synthesis of monoaryl epoxides, cyclopropanes, and aziridines. The (1S,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. © 2004 Wiley‐Liss, Inc.