You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
Can you give the molecular formula of the molecule (5R)-5-[2-(4-chlorophenyl)-2-[6-methoxy-5-(1H-pyrazol-4-yl)pyridin-2-yl]ethenyl]pyrrolidin-2-one ?
user
C21H19ClN4O2
assistant