title: Crystallization-induced diastereomeric transformation of N-2'-t-butyl-6'-iodobenzoyl-3-bromocarbazole.
abstract: We previously reported the atropisomeric properties of 2'-t-butyl-6'-iodo-substituted N-benzoyl-3-bromocarbazole, i.e., the steric or electronic effects of the substituents restricted the rotation about the N-C7' and C7'-C1' bonds to separate four stereoisomers (cis/trans for the N-C7' axis, aR/aS for the C7'-C1' axis). Furthermore, the 2'-t-butyl-6'-iodo-substituted N-benzoyl 3-bromocarbazole was confirmed to be a gear molecule, in which the rotation about the C7'-C1' bond was in perfect concert with that about the N-C7' bond. Herein, we report a unique crystallization-induced diastereomeric transformation found in this molecule. In the isolation process, where the product is recrystallized from the diastereoisomeric mixture, in situ isomerization and selective crystallization could lead to a diastereomeric transformation, and a mixture of diastereomers (trans/cis=54 : 46) was converted to trans-isomer-enriched crystals (trans/cis>96 : 4) in 95% yield. Conformational analysis clarified the preference for the trans versus cis isomer.
authors.affiliation: School of Pharma Sciences, Teikyo University.
authors.forename: Susumu
authors.initials: S
authors.lastname: Kayama
authors.forename: Norihiko
authors.initials: N
authors.lastname: Tani
authors.forename: Yuka
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Hidetsugu
authors.initials: H
authors.lastname: Tabata
authors.forename: Shintaro
authors.initials: S
authors.lastname: Wakamatsu
authors.forename: Tetsuta
authors.initials: T
authors.lastname: Oshitari
authors.forename: Hideaki
authors.initials: H
authors.lastname: Natsugari
authors.forename: Hideyo
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D002227:Carbazoles / Q000737:chemistry*; D003460:Crystallization; D054879:Halogenation; D008958:Models, Molecular; D013237:Stereoisomerism
chemical_list: D002227:Carbazoles