Phosphorus oxychloride → (R)-4-chloro-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine

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Reaction Steps

Neat POCl3 (463.9 ml, 5067 mmol) was added slowly by addition funnel to a 0° C. solution of (R)-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-ol (152.2 g, 1013 mmol) in DCE (1.2 L). After the addition was complete, the reaction mixture was warmed to room temperature, then heated to reflux and stirred for 70 minutes. The reaction was complete as determined by HPLC. The reaction mixture was cooled to room temperature, and the excess POCl3 was quenched in 4 portions as follows: Reaction mixture transferred to separatory funnel and dripped into a beaker containing ice and saturated NaHCO3 solution cooled in an ice bath. Once the addition of each portion of the reaction mixture was completed, the quenched mixture was stirred 30 minutes to ensure complete destruction of POCl3 prior to transfer to separatory funnel. The mixture was transferred to the separatory funnel and extracted twice with DCM. The combined extracts were dried (Na2SO4), filtered, and concentrated. The crude was purified on silica gel as follows: silica gel (1 kg) was slurried in 9:1 hexane:ethyl acetate onto a 3 L fitted funnel, silica settled under vacuum, topped with sand. The crude was loaded with a DCM/hexane mixture, and the compound was eluted using 1 L sidearm flasks under vacuum. High Rf byproducts eluted first, then (R)-4-chloro-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine (104.4 g, 61.09% yield) as a brown oil. Triethylamine (93.0 ml, 534 mmol) and tert-butyl piperazine-1-carboxylate (34.8 g, 187 mmol) was added to a solution of (R)-4-chloro-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine (30.0 g, 178 mmol) in n-BuOH (250 mL). The reaction mixture was heated to reflux under nitrogen and stirred overnight (17 hours), after which it was concentrated on a rotavap. The resulting oil was dissolved in DCM, washed with H2O, dried (Na2SO4), filtered, and was concentrated. The resulting brown oil was purified on silica gel eluting first with 2:1 hexanes:ethyl acetate until product eluting cleanly, then gradient 1:1 to 1:5 DCM:ethyl acetate to give (R)-tertbutyl 4-(5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-yl)piperazine-1-carboxylate (42.0 g, 74.1% yield) as a beige powder. LC/MS (APCI+) m/z 319.1 [M+H]+.

Provenance & Evidence