3-(2-Chloroethyl-d4)-2-methyl-9-(benzyloxy)-4H-pyrido[1,2a]pyrimidin-4-one is an intermediate in the synthesis of 9-Hydroxy Risperidone-d4 (H953352), a deuterated metabolite of Risperidone (R525000), a combined serotonin (5-HT2) and dopamine (D2) receptor antagonist.