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Structural and Rate Studies of the 1,2-Additions of Lithium Phenylacetylide to Lithiated Quinazolinones: Influence of Mixed Aggregates on the Reaction Mechanism
journal contribution
posted on 2004-05-05, 00:00 authored by Timothy F. Briggs, Mark D. Winemiller, David B. Collum, Rodney L. Parsons,, Akin H. Davulcu, Gregory D. Harris, Joseph M. Fortunak, Pat N. ConfaloneThe 1,2-addition of lithium phenylacetylide (PhCCLi) to quinazolinones was investigated using
a combination of structural and rate studies. 6Li, 13C, and 19F 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 19F 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.
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19 F NMR spectroscopies showrate studieslithium phenylacetylide13 Clithium hexamethyldisilazideLithium Phenylacetylidetrisolvated PhCCLi monomersRate Studiesreaction ratesdependencePhCCLi concentrationquinazolinoneambient temperaturesPhCCLi dimerTHF concentrationsrate lawMixed Aggregates6 Lidisolvated PhCCLi monomer19 F NMR spectroscopyReaction Mechanism
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