A metastable, polymorphic hexameric crystal structure of lithium pinacolone enolate (LiOPin) is reported along with three preparation methods. NMR-based structural characterization implies that the lithium pinacolate hexamer deaggregates to a tetramer in toluene but retains mainly the hexameric structure in nonaromatic hydrocarbon solvents such as cyclohexane. Moreover, the presence of a small amount of lithium aldolate (LiOA) dramatically influences the aggregation state of LiOPin by forming a mixed aggregate with a 3:1 ratio (LiOPin·LiOA).
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Conformational Polymorphism of Lithium Pinacolone Enolate.
J Am Chem Soc
November 2016
Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States.
A metastable, polymorphic hexameric crystal structure of lithium pinacolone enolate (LiOPin) is reported along with three preparation methods. NMR-based structural characterization implies that the lithium pinacolate hexamer deaggregates to a tetramer in toluene but retains mainly the hexameric structure in nonaromatic hydrocarbon solvents such as cyclohexane. Moreover, the presence of a small amount of lithium aldolate (LiOA) dramatically influences the aggregation state of LiOPin by forming a mixed aggregate with a 3:1 ratio (LiOPin·LiOA).
View Article and Find Full Text PDFLithium pinacolone enolate solvated by hexamethylphosphoramide.
J Am Chem Soc
June 2015
Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States.
We report the crystal structure of a substoichiometric, HMPA-trisolvated lithium pinacolone enolate tetramer (LiOPin)4·HMPA3 abbreviated as T3. In this tetramer one HMPA binds to lithium more strongly than the other two causing a reduction in spatial symmetry with corresponding loss of C3 symmetry. A variety of NMR experiments, including HMPA titration, diffusion coefficient-formula weight (D-FW) analysis, and other multinuclear one- and two-dimensional NMR techniques reveal that T3 is the major species in hydrocarbon solution when more than 0.
View Article and Find Full Text PDFPalladium-catalyzed tandem reactions to form 1-vinyl-1h-isochromene derivatives.
J Org Chem
May 2001
Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
The palladium-catalyzed reaction of pinacolone with tert-butyldimethyl(3-(2-bromophenyl)allyloxy)silane results in direct formation of 1-vinyl-3-tert-butyl-1H-isochromene. This is the result of a ketone arylation followed by an intramolecular cyclization of the enolate with the allylic system. The use of a lithium diamide base appears to be essential for success.
View Article and Find Full Text PDFReactions of PhSCH(2)Li and NCCH(2)Li with benzaldehyde and benzophenone: when does the mechanism change from ET to polar?
J Org Chem
March 2001
Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan.
The carbonyl-carbon kinetic isotope effect (KIE) and the substituent effect were measured for the reaction of phenylthiomethyllithium (PhSCH(2)Li, 1) with benzaldehyde and benzophenone, and cyanomethyllithium (NCCH(2)Li, 2) with benzaldehyde, and the results were compared with those for other lithium reagents such as MeLi, PhLi, CH(2)=CHCH(2)Li, and CH(2)=C(OLi)C(CH(3))(3). It was previously shown that the reactions of MeLi, PhLi, and CH(2)=CHCH(2)Li proceed via a rate-determining electron transfer (ET) process whereas the reaction of lithium pinacolone enolate goes through the polar (PL) mechanism. The reaction of 1 with benzaldehyde gave no carbonyl-carbon KIE ((12)k/(13)k = 0.
View Article and Find Full Text PDFHigh yields of potential glycol metabolites of p-synephrine, epinephrine, octopamine, and normacromerine can be obtained from the readily available monosubstituted and disubstituted acetophenones. The general procedure involves alpha-bromination followed by displacement with acetate ion and reduction with lithium aluminum hydride. Yields ranged from 46 to 91%.
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