Regioselective addition of Grignard reagents to -acylpyrazinium salts: synthesis of substituted 1,2-dihydropyrazines and Δ-2-oxopiperazines.

The regioselective addition of Grignard reagents to mono- and disubstituted -acylpyrazinium salts affording substituted 1,2-dihydropyrazines in modest to excellent yields (45-100%) is described. Under acidic conditions, these 1,2-dihydropyrazines can be converted to substituted Δ-2-oxopiperazines providing a simple and efficient approach towards their preparation.