Four-Component Synthesis of Polysubstituted Pyrazin-2(1H)-ones through a Ugi/Staudinger/Aza-Wittig/Isomerization Sequence.

A new efficient synthesis of polysubstituted pyrazin-2(1H)-ones via the sequential Ugi/Staudinger/aza-Wittig/isomerization reaction has been developed. The four-component Ugi reactions of arylglyoxals 1, primary amines 2, α-azidovinyl acids 3, and isocyanides 4 produced the azides 5, which were treated with triphenylphosphine to give pyrazin-2(1H)-ones 6 in good yields through domino Staudinger/aza-Wittig/isomerization reactions.