title: Asymmetric iodocyclization catalyzed by salen-CrIIICl: its synthetic application to swainsonine.
abstract: The previously developed enantioselective iodocyclization of gamma-hydroxy-cis-alkenes required 30 mol% of (R,R)-salen-Co(II) complex as chiral catalyst and 0.75 equivalent of N-chlorosuccinimide (NCS) as activator to produce 2-substituted tetrahydrofurans with 61 to 90% ee. Due to the considerable loading amount of the Co(II) complex, another more effective catalyst was pursued by screening (R,R)-salen-transition metal complexes. When 10 mol% of the catalysts were applied with 0.5 equivalent of NCS, a higher level of stereoselectivity was attained with the corresponding Cr(III)Cl (84% ee), Mn(II)Cl (52% ee) and Co(II) complexes (66% ee). Refinement of the conditions established a novel catalytic enantioselective iodocyclization protocol using iodine in the presence of 7 mol% of (R,R)-salen-Cr(III)Cl complex activated by 0.7 equivalent of NCS in toluene to induce 74 to 93% ee.
authors.affiliation: Center for Molecular Design and Synthesis, Department of Chemistry, School of Molecular Science (BK21), KAIST, Daejeon 305-701, Korea.
authors.forename: Hyo Young
authors.initials: HY
authors.lastname: Kwon
authors.forename: Chul Min
authors.initials: CM
authors.lastname: Park
authors.forename: Sung Bae
authors.initials: SB
authors.lastname: Lee
authors.forename: Joo-Hack
authors.initials: JH
authors.lastname: Youn
authors.forename: Sung Ho
authors.initials: SH
authors.lastname: Kang
mesh_terms: D002384:Catalysis; D002712:Chlorides / Q000737:chemistry*; D002857:Chromium / Q000737:chemistry*; D003500:Cyclization; D005029:Ethylenediamines / Q000737:chemistry*; D007455:Iodine / Q000737:chemistry*; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D017026:Swainsonine / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D002712:Chlorides; D005029:Ethylenediamines; D009942:Organometallic Compounds; D002857:Chromium; C011452:disalicylaldehyde ethylenediamine; D007455:Iodine; D017026:Swainsonine