Synthesis, spontaneous racemization, and photoisomerization of benzo[e]pyrene 9,10-oxide

Abstract

Benzo[e]pyrene 9,10-oxide (4) and the isomeric pyreno[4,5-b]oxepine (9) have been simultaneously synthesized from racemic and optically active bromo acetate precursors of known absolute configurations. Spontaneous thermal racemization of benzo[e]pyrene 9,10-oxide (4)[via the undetected oxepine intermediate (15)], and readily occurring photoisomerization of this arene oxide [via the putative arene oxide intermediate (16) to yield pyreno[4,5-b]oxepine (9)] occur as predicted from PMO calculations of resonance energy changes associated with these pericyclic reactions. Optically pure samples of the mammalian metabolites 9,10-epoxy-(12) and trans-9,10-dihydroxy-9,10,11,12-tetrahydrobenzo[e]pyrene (13) have been obtained.