Regioselective Reduction of 3-Substituted N-Acylpyrazinium Salts toward the Synthesis of 1,2-Dihydropyrazines

Regioselective addition of Grignard reagents to N-acylpyrazinium salts: synthesis of substituted 1,2-dihydropyrazines and Δ5-2-oxopiperazines

The regioselective addition of Grignard reagents to mono- and disubstituted N-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 Δ⁵-2-oxopiperazines providing a simple and efficient approach towards their preparation.

Synthesis, antimycobacterial and antifungal evaluation of some new 1-ethyl-5-(hetero)aryl-6-styryl-1,6-dihydropyrazine-2,3-dicarbonitriles

The Petasis reaction of 6-hydroxy adducts of 1-alkyl-2,3-dicyano-5-arylpyrazinium salts with trans-styrylboronic acids proved to proceed smoothly at room temperature to give the corresponding 5-(hetero)aryl-6-styryl substituted 1,6-dihydropyrazine derivatives. Also it has been found that C(6) unsubstituted 1,6-dihydro- or 1,4,5,6-tetrahydropyrazine derivatives can be easy prepared in high yields from the corresponding pyrazinium salts by reduction with triethylsilane. All synthesized compounds were screened in vitro for their antifungal activities against seven pathogenic fungal strains and antimycobacterial activities against Mycobacterium tuberculosis H37Rv, avium, terrae and multi-drug-resistant strains isolated from tuberculosis patients in the Ural region (Russia).