Regioselectivity in lithiation of 1-methylpyrazole: experimental, density functional theory and multinuclear NMR study.
Reaction of 1-methylpyrazole with n-BuLi in THF followed by reaction with monodeuteromethanol (CH3OD) under kinetically controlled conditions leads to functionalisation at the methyl group, whereas reaction under thermodynamically controlled conditions leads to functionalisation at the pyrazole 5-position. The observed regioselectivity can be correctly predicted, at least qualitatively, using density functional B3LYP/6-31+G(d,p) calculations only when solvation effects (IEFPCM) are taken into account. The 1H,6Li HOESY and NOESY NMR spectra of the thermodynamic product 5-lithio-1-methylpyrazole (5-Li) in [D8]THF are consistent with an oligomeric structure.
Department of Medicinal Chemistry, Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100, Copenhagen, Denmark. tb@dfuni.dk
Thomas
T
Balle
Mikael
M
Begtrup
Jerzy W
JW
Jaroszewski
Tommy
T
Liljefors
Per-Ola
PO
Norrby
D007700:Kinetics; D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011720:Pyrazoles / Q000737:chemistry*; D013816:Thermodynamics
D011720:Pyrazoles; D008094:Lithium