Rac-7-oxopramipexole, an impurity reference during the quality study of pramipexole, was synthesized from 1,3-cyclohexanedione by bromination with bromine, cyclization with thiourea, bromination and substitution with sodium azide to give 2-amino-6-azido-7-oxo-4,5,6,7-tetrahydrobenzothiazole (6), which was subjected to successive reduction with sodium borohydride and zinc powder, reductive amination with n-propanal and sodium triacetoxyborohydride, followed by oxidation with PCC with an overall yield of about 11.7%.