Stoichiotnetric Dependence of the Long-Established Reaction of Butyllithium with Pyridine: A Hidden Secondary Reaction That Produces a Pyridine Adduct of a Lithiodihydropyridine

摘要

Over 60 years ago Ziegler first recognized the value of alkyllithium compounds in convening pyridine to 2-alkyl-substituted derivalives. However. only recently has the reactive intermediate in such processes, a solvated nitrogen-lithium adducl 1, beenisolated and studied directly. Examination of the adduet 1 revealed that addition is accompanied by bis-(pyridine) solvation of the nitrogen-attached metal center, which requires a n-butyllithium: pyridine ratio of 1:3. As reported here, by using more than a threefold molar excess of the heterocycle. we have uncovered a remarkable secondary reaction which, despite the age of and considerable attention given to this chemistry, had previously gone unnoticed. Formally the new reaction involves reduction of pyridine by lithium hydride, though it is certain that the conventional ionic solid does not form during the process. The isolated product 2, characterized both in the crystal and in solution, is a novel bis(pyridine)-dihydropyridyllithium dimer.