Synthesis of 5-methyl-6,7-dihydro-5H-cyclopentapyrazine

Cyclopenapyrazine compounds have important sensory properties in food and tobacco smoke.With anhydrous ethanol as solvent,manganese dioxide as oxidant,5-methyl-6,7-dihydro-5H-cyclopentapyrazine(Compound 2) was synthesized by methyl cyclopentenolone and ethylenediamine via condensation cyclization and oxidation.Moreover,the synthesis conditions were optimized,and the structures of the products were characterized by ¹H NMR and IR.The results showed that the yield of 5-methyl-3,4,6,7-tetrahydro-2H-cyclopentapyrazine(Compound 1) was 95.7% under the optimized conditions of anhydrous ethanol 20 mL,n(methyl cyclopentenolone):n(ethylenediamine)=1:1.5,reacting for 2 hours at a constant temperature of 60℃.When n(potassium hydroxide):n(manganese dioxide):n(Compound 1)=1:2.4:0.6 and the amount of anhydrous ethanol was 10 mL,the yield of Compound 2 reached 64.3% after reacting for 15 hours at 80℃.