You are a chemist. Please follow the instructions to convert the structure to the corresponding name.
system
What is the molecular formula of the molecule identified by (4R,4aS,12bR)-9-methoxy-7a-methyl-4a-propoxy-2,3,4,5,6,13-hexahydro-1H-4,12-methanobenzofuro[3,2-e]isoquinolin-7-one ?
user
C21H27NO4
assistant