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 1-(1,3,4,6,7,8,9,9a-octahydropyrido[1,2-a]pyrazin-2-yl)-2-chloro-2-phenylethanone .
user
C16H21ClN2O
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