Selective Reduction of Pyridazin-3-ones and Ring Contraction to Pyrrolidin-2-ones and 3-Pyrrolin-2-ones ... George R. Brown," Alan J. Foubister, and Brian Wright ICI Pharmaceuticals Division, Alderle y Park, Macclesfield, Cheshire, SK I0 4TG, UK ... Reduction of pyridazin-3-ones (la-d) with zinc dust in acetic acid affords selectively 4,5-di hydropyridazin-3-ones (2a-d), but N(2)-substituted (1) react further with excess of zinc to give equal amounts of pyrrolidin-2- ...