1-Methyl-2-piperidinone 1-Methyl-2-piperidone 2-Piperidinone, 1-methyl- 2-Piperidone, 1-methyl- 931-20-4 N-Methyl-.delta.-valerolactam N-Methyl-2-piperidinone N-Methyl-2-piperidone NSC67384