Total chemical synthesis of 2-ethenyl-3,5-dimethylpyrazine and 3-ethenyl-2,5-dimethylpyrazine

The aroma compounds 2-ethenyl-3,5-dimethylpyrazine and 3-ethenyl-2,5-dimethylpyrazine were synthesized via a new chemical route. The key steps of the synthesis involve cyclocondenzation of 1-[bicyclo[2.2.1]5-hepten-2-yl]-1,2-propanedione and 1,2-propanediamine, aromatization of the resulting 5,6-dihydropyrazines, and subsequent Retro-Diels–Alder reaction to generate pyrazines and . Pyrazine , a powerful odorant, was obtained in large excess (8:2) when endo-1-[bicyclo[2.2.1]5-hepten-2-yl]-1,2-propanedione was used as intermediate substrate.