Kröhnke Pyridine Synthesis

W. Zecher, F. Kröhnke, Ber. 94, 690, 698 (1961); eidem, Angew. Chem. Int. Ed. 1, 626 (1962).

1,4-Michael addition, q.v., of α-pyridinium methyl ketone salts to α,β-unsaturated ketones, generating the 1,5-dicarbonyl compounds which undergo ammonium acetate-promoted ring closure, to yield substituted pyridines:

Early review: F. Kröhnke, Synthesis 1976, 1-24. Synthetic applications: J. N. Chatterjea et al., Indian J. Chem. 15B, 430 (1977); G. R. Newkome et al., J. Org. Chem. 51, 850 (1986); P. Lhoták, A. Kurfürst, Coll. Czech. Chem. Commun. 57, 1937 (1992); T. R. Kelly et al., J. Org. Chem. 62, 2774 (1997). Cf. Chichibabin Pyridine Synthesis; Guareschi-Thorpe Condensation; Hantzsh (Dihydro)Pyridine Synthesis.