(3R,4R)-tert-Butyl 4-Methyl-3-(methyl(7H-pyrrolo[2,3-d]pyrimidin-4-yl)amino)piperidine-1-carboxylate is an intermediate in the synthesis of 5,6-Dihydro CP-690550 (D450240), an impurity of CP-690550 (C781350), a pyrrolo[2,3-d]pyrimidine derivative, as Janus kinase inhibitor for treatment of rheumatoid arthritis.