Lithium-mediated zincation of pyrazine, pyridazine, pyrimidine, and quinoxaline.
Deprotonation of pyrazine, pyridazine, pyrimidine, and quinoxaline using an in situ mixture of ZnCl2.TMEDA (0.5 equiv) and LiTMP (1.5 equiv) was studied. Pyrazine and pyrimidine were deprotonated in THF at room temperature, a result evidenced by trapping with I2. The competitive formation of dimer observed in net hexane was reduced by using cosolvents (TMEDA or THF). Starting from quinoxaline, the dimer formation took place in THF also, and mixtures of mono- and diiodides were obtained whatever the solvent and conditions used. A similar competitive formation of a diiodide was noted with pyridazine; the use of THF at reflux temperature nevertheless afforded the 3-iodo derivative in good yield.
Seggio
Anne
A
Synthèse et ElectroSynthèse Organiques, UMR 6510 CNRS, Université de Rennes 1, Bâtiment 10A, Case 1003, Campus Scientifique de Beaulieu, 35042 Rennes Cedex, France.
Chevallier
Floris
F
Vaultier
Michel
M
Mongin
Florence
F
D008094:Lithium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D011719:Pyrazines / Q000737:chemistry*; D011724:Pyridazines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*; D011810:Quinoxalines / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
D011719:Pyrazines; D011724:Pyridazines; D011743:Pyrimidines; D011810:Quinoxalines; C062482:pyridazine; D008094:Lithium; D015032:Zinc; C030986:pyrimidine