N,N-diacyl-1,4-dihydropyrazine　derivatives　(1)　were　prepared　via　an　efficient　microwave-assisted　synthesis.　1　was　isolated　and　unambiguously　confirmed　by　NMR　spectra　and　high-resolution　mass　spectrometry.　The　NMR　spectra　of　1　showed　complicated　rather　than　conventional　spectroscopy.　Variable　temperature　experiments　and　DFT　calculation　(PES)　were　used　to　investigate　this　phenomenon.　DFT　calculations　confirmed　that　the　structures　of　the　two　rotamers　of　I　correspond　to　those　determined　by　NMR　in　solution,　and　gave　the　syn-anti　interconversion　barriers　of　rotamers.　The　results　showed　that　two　isomers　exist　in　solution　(deuterated　solvent)　at　room　temperature,　resulting　in　complicated　NMR　spectra.　(C)　2017　Elsevier　B.V.　All　rights　reserved.