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Paper | Special issue | Vol 35, No. 1, 1993, pp.151-169
Published online, 1st January, 1970
DOI: 10.3987/COM-92-S1
Regioselective ortho-Lithiation of Halopyridines. Syntheses of ortho-Disubstituted Pyridines and a Convenient Generations of 3,4-Pyridyne

Gordon W. Gribble* and mark G. Saulnier

*Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03775, U.S.A.

Abstract

The regioselective ortho-lithiation of 3-chloro- (4), 3-fluoro- (7), 3-bromo- (10), 2-chloro- (22), and 4-chloropyridine (25) with lithium diisopropylamide affords, after quenching with various electrophiles, the corresponding ortho-disubstituted pyridines in yields from 16-96%. Halogen-metal exchange between 4-iodo-3-chloropyridine (6a) and tert-butyllithium or n-butyllithium provides a convenient generation of 3,4-pyridyne (1), which is trapped in a Diels-Alder reaction with furan and 2,5-dimethylfuran to give 31 and 32 (24-38%).