title: Structural and rate studies of the 1,2-additions of lithium phenylacetylide to lithiated quinazolinones: influence of mixed aggregates on the reaction mechanism.
abstract: The 1,2-addition of lithium phenylacetylide (PhCCLi) to quinazolinones was investigated using a combination of structural and rate studies. (6)Li, (13)C, and (19)F NMR spectroscopies show that deprotonation of quinazolinones and phenylacetylene in THF/pentane solutions with lithium hexamethyldisilazide affords a mixture of lithium quinazolinide/PhCCLi mixed dimer and mixed tetramer along with PhCCLi dimer. Although the mixed tetramer dominates at high mixed aggregate concentrations and low temperatures used for the structural studies, the mixed dimer is the dominant form at the low total mixed aggregate concentrations, high THF concentrations, and ambient temperatures used to investigate the 1,2-addition. Monitoring the reaction rates using (19)F NMR spectroscopy revealed a first-order dependence on mixed dimer, a zeroth-order dependence on THF, and a half-order dependence on the PhCCLi concentration. The rate law is consistent with the addition of a disolvated PhCCLi monomer to the mixed dimer. Investigation of the 1,2-addition of PhCCLi to an O-protected quinazolinone implicates reaction via trisolvated PhCCLi monomers.
authors.affiliation: Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Briggs
authors.forename: Mark D
authors.initials: MD
authors.lastname: Winemiller
authors.forename: David B
authors.initials: DB
authors.lastname: Collum
authors.forename: Rodney L
authors.initials: RL
authors.lastname: Parsons
authors.forename: Akin H
authors.initials: AH
authors.lastname: Davulcu
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Harris
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Fortunak
authors.forename: Pat N
authors.initials: PN
authors.lastname: Confalone
mesh_terms: D019281:Dimerization; D007700:Kinetics; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011799:Quinazolines / Q000737:chemistry*; D013696:Temperature
chemical_list: D011799:Quinazolines; D008094:Lithium