You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Provide the molecular formula for the IUPAC named substance methyl 1-[4-[(4-chlorobenzoyl)amino]butanoyl]-2,3,3a,4,5,6,7,7a-octahydroindole-2-carboxylate .
user
C21H27ClN2O4
assistant