Formic Acid → tert-Butyl 4-((5R,7S)-7-hydroxy-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-yl)piperazine-1-carboxylate

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Reaction Steps

Triethylamine (4.33 mL, 31.1 mmol) (degassed with nitrogen 30 minutes prior to use) and formic acid (1.36 mL, 36.1 mmol) (degassed with nitrogen 30 minutes prior to use) were added to a solution of (R)-tert-butyl 4-(5-methyl-7-oxo-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-yl)piperazine-1-carboxylate (9.75 g, 29.3 mmol) in DCM (210 mL; degassed with nitrogen 30 minutes prior to use). The reaction mixture was stirred for 5 minutes, and then a Ru catalyst (0.0933 g, 0.147 mmol) was added. The reaction was stirred under positive nitrogen pressure overnight (18 hours). The reaction mixture was concentrated to dryness and dried on a high vacuum. 1H NMR of the crude looked like 85% diastereoselectivity. The crude was flashed on Biotage 65M (loaded 1:1 DCM:ethyl acetate 500 mL flushed, then 1:4 DCM:ethyl acetate until product (2nd spot), then gradient to neat ethyl acetate, then 25:1 DCM:MeOH eluted rest of product. The fractions were combined and concentrated on a rotary evaporator. The residue was concentrated again from DCM/hexanes to give a mixture of tert-butyl 4-((5R,7R)-7-hydroxy-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-yl)piperazine-1-carboxylate (major) and tert-butyl 4-((5R,7S)-7-hydroxy-5-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidin-4-yl)piperazine-1-carboxylate (minor) (9.35 g, 95.3% yield) as a beige foam. LC/MS (APCI+) m/z 335 [M+H]+. 1H NMR (CDCl3) shows 88% diastereoselectivity by integration of carbinol methine.

Provenance & Evidence