You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Please write the molecular formula of the molecule propan-2-yl (4aR,7aS)-1-[(3-methoxyphenyl)methyl]-6,6-dioxo-2,3,4a,5,7,7a-hexahydrothieno[3,4-b]pyrazine-4-carboxylate .
user
C18H26N2O5S
assistant