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 6'-[(4-methylpiperazin-1-yl)methyl]-2'-phenylspiro[1,3-dioxa-2lambda4-thiacyclohept-5-ene-2,1'-imidazo[2,1-b][1,3]thiazole]-4,7-dione .
user
C21H22N4O4S
assistant