title: Towards configurationally stable [4]helicenes: enantioselective synthesis of 12-substituted 7,8-dihydro[4]helicene quinones.
abstract: The synthesis of enantiopure C-12 methoxy- or alkyl-substituted 5,7,8,12b-tetrahydro[4]helicene quinones 16 and 17 and the 7,8-dihydroaromatic analogues 4 and 5 has been achieved from (SS)-2-(p-tolylsulfinyl)-1,4-benzoquinone. In the first series, with a structure containing both central and helical chiralities, the R absolute configuration of the stereogenic carbon atom was defined after the asymmetric cycloaddition step, whereas the P or M helicity was shown to be dependent on the nature of the C-12 substituent. The size of this group was also defining the configurational stability of the final (P)-7,8-dihydro[4]helicene quinones 4 and 5. The interconversion barriers between the P and M helimers in the latter, computed with a DFT B3LYP method, matched well with the experimentally observed stability. Our study provided evidence that, in addition to steric effects, a small but significant role of electronic effects is governing the configurational stability of such helical quinones.
authors.affiliation: Departamento de Química Orgánica C-I, Universidad Autónoma Madrid, Cantoblanco, 28049 Madrid, Spain. carmen.carrenno@uam.es
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Carreño
authors.forename: Alvaro
authors.initials: A
authors.lastname: Enríquez
authors.forename: Susana
authors.initials: S
authors.lastname: García-Cerrada
authors.forename: M Jesús
authors.initials: MJ
authors.lastname: Sanz-Cuesta
authors.forename: Antonio
authors.initials: A
authors.lastname: Urbano
authors.forename: Feliu
authors.initials: F
authors.lastname: Maseras
authors.forename: Alfons
authors.initials: A
authors.lastname: Nonell-Canals
mesh_terms: D018360:Crystallography, X-Ray; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000138:chemical synthesis*; D011809:Quinones / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D011083:Polycyclic Compounds; D011809:Quinones; C031660:helicenes