title: Stereoselective synthesis of atropisomeric korupensamines A and B utilizing planar chiral arene chromium complex.
abstract: Naphthyl tetrahydroisoquinoline alkaloids, atropisomeric korupensamines A and B and ent-korupensamine B, were synthesized by syn-selective cross-coupling of a planar chiral arene chromium complex with naphthylboronic acid and subsequent axial isomerization or tricarbonylchromium migration to the inverted arene face as a key step. Palladium(0)-catalyzed cross-coupling of planar chiral arene chromium complex 12 with naphthylboronic acid 9 gave syn-biaryl coupling product 13. syn-Biaryl chromium complex 13 was heated in 1:1 mixture of di-n-butyl ether and 1,2-dichloroethane to give a face-inverted anti-biaryl chromium complex 14 without axial isomerization. Korupensamine A was synthesized from the syn-biaryl chromium complex 13 via o-formyl syn-biaryl chromium complex 10, and ent-korupensamine B was prepared from the face-inverted anti-biaryl chromium complex 14. On the other hand, difluoro-substituted syn-biaryl chromium complex 40 with a formyl group afforded anti-biaryl chromium complex 41 containing a rotated central bond by heating in xylene. The chromium-complexed fluorine atom was easily substituted with an isopropoxy group by nucleophilic substitution. Use of these reactions allowed (+)-2-bromo-3,5-difluorobenzaldehyde chromium complex (37) as a single chiral source to be converted to atropisomeric korupensamines A and B, respectively.
authors.affiliation: Department of Chemistry, Faculty of Integrated Arts and Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Yoshie
authors.initials: Y
authors.lastname: Tanaka
authors.forename: Ryohei
authors.initials: R
authors.lastname: Shoda
authors.forename: Ryota
authors.initials: R
authors.lastname: Sakamoto
authors.forename: Ken
authors.initials: K
authors.lastname: Kamikawa
authors.forename: Motokazu
authors.initials: M
authors.lastname: Uemura
mesh_terms: D017608:Chromium Compounds / Q000737:chemistry*; D007546:Isoquinolines / Q000138:chemical synthesis*; D009281:Naphthalenes / Q000138:chemical synthesis*; D013237:Stereoisomerism
chemical_list: D017608:Chromium Compounds; D007546:Isoquinolines; D009281:Naphthalenes; C110657:korupensamine A