title: Light-induced enantiospecific 4π ring closure of axially chiral 2-pyridones: enthalpic and entropic effects promoted by H-bonding.
abstract: Nonbiaryl axially chiral 2-pyridones were synthesized and employed for light-induced electrocyclic 4π ring closure leading to bicyclo-β-lactam photoproducts in solution. The enantioselectivity in the photoproducts varied from 22 to 95% depending on the reaction temperature and the ability of the axially chiral chromophore to form intramolecular and/or intermolecular H-bonds with the solvent. On the basis of the differential activation parameters, entropic control of the enantiospecificity was observed for 2-pyridones lacking the ability to form H-bonds. Conversely, enthalpy played a significant role for 2-pyridones having the ability to form H-bonds.
authors: Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108, USA.
authors: Elango
authors: E
authors: Kumarasamy
authors: Josepha L
authors: JL
authors: Jesuraj
authors: Joseph N
authors: JN
authors: Omlid
authors: Angel
authors: A
authors: Ugrinov
authors: Jayaraman
authors: J
authors: Sivaguru
mesh_terms: D018360:Crystallography, X-Ray; D003500:Cyclization; D006860:Hydrogen Bonding; D008027:Light; D008958:Models, Molecular; D015394:Molecular Structure; D011728:Pyridones / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D011728:Pyridones; C017679:2-hydroxypyridine