p-Toluenesulfonic acid monohydrate → HCID 67007910, compound

Participants

Reaction Steps

To a solution of 1-benzyl-3-methylpiperidin-4-one (Acros, 62.09 g, 305.4 mmol) and (2S,4S)-pentane-2,4-diol (TCI-US, 34.06 g, 327.0 mmol) in benzene (800 mL) was added p-toluenesulfonic acid mono hydrate (69.72 g, 404.9 mmol). The flask was fitted with a Dean-Stark trap and heated to reflux. The reaction mixture was cooled after 16 hours of reflux, concentrated to a total volume of about 500 mL and transferred to an Erlenmeyer flask with ethyl acetate. A sodium bicarbonate solution (500 mL) added with stirring and the mixture was further neutralized with solid Na2CO3 (35 g). The layers were partitioned, the organic phase washed with sodium bicarbonate, dried (Na2SO4) and concentrated to yield approximately 95 g of crude material. The residue was purified in 15 g batches by silica gel chromatography (Analogix SF-65-600 g; 35 micron silica; elution with 10% ethyl acetate-hexane) at 50 mL/min to provide 42.33 g of the first eluting isomer, (2S,4S,7R)-9-benzyl-2,4,7-trimethyl-1,5-dioxa-9-azaspiro[5.5]undecane. 1H NMR (300 MHz, DMSO-d6) δ 7.33-7.19 (m, 5H), 4.07-3.86 (m, 2H), 3.40 (ABq, 2H, JAB=13.5 Hz, δνAB=23.3 Hz), 2.41-2.20 (m, 4H), 1.90-1.76 (m, 2H), 1.59-1.47 (m, 3H), 1.12 (d, 3H, J=6.4 Hz), 1.11 (d, 3H, J=6.4 Hz), 0.90 (d, 3H, J=7.1 Hz); MS (DCI/NH3) m/e 290 (M+H)+.

Provenance & Evidence