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4-Phenyl-2-N-(R-(−)-α-(2-naphthyl)ethylamino)-1-thia-1,3-dienes when activated by acetyl chloride, undergo extremely efficient diastereoselective exo Diels-Alder cycloadditions giving access to thiopyrans of high optical purity.

A novel Pd(0)-catalyzed carbonylation of both isolable 1,2-diaza-1,3-butadienes and those generated in situ by extrusion of SO2 and CO2 from heterocyclic precursors is described. The reaction proceeds at room temperature to 110 °C under 1−2 atm of CO to afford 2,3-pyrazol-1(5H)-ones in good to excellent yields. The effect of catalyst structure and stability on the carbonylation reaction is evaluated.

[reaction--see text] [corrected] The preparation and thermolysis of new stable heterocyclic precursors of 1,2-diaza-1,3-butadienes is described. The resulting reactive diazadienes are trapped in situ with N-phenylmaleimide [corrected]. The effect of precursor structure on the temperature at which the diazadienes are generated is discussed.