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 (1 R ,2 R ) 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 LiAlH 4 . 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 (1 S ,2 R )‐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 CH 2 ‐aryl (phenanthryl or anthryl), which is critical when the tweezer method is applied for absolute configurational assignment (phenyl = medium group; anthacenyl CH 2 and phenanthryl CH 2 = large group). Chirality 16:196–203, 2004. © 2004 Wiley‐Liss, Inc.