Trifluoroacetic acid → Ethyl 4-cyanomethyl-2-piperidinecarboxylate

Participants

Reaction Steps

To a solution of 19.9 g (67.2 mmol) of ethyl 4-cyanomethyl-N-t-butoxycarbonyl-2-piperidinecarboxylate (prepared in Example 3F) in 100 ml of dichloromethane was added 50 ml of trifluoroacetic acid (CO2 evolution). The mixture was stirred for 3 hr at room temperature and then was concentrated under vacuum. To the residue was added 100 ml of dichloromethane, and the solution was again concentrated under vacuum. The residue was dissolved in 200 ml of dichloromethane, 200 ml of saturated aqueous sodium bicarbonate was added, and the mixture was stirred for 15 minutes at room temperature. The organic layer was separated and washed with 100 ml of saturated aqueous sodium bicarbonate, and the combined aqueous washes were extracted twice with 100 ml each of dichloromethane and once with 50 ml of diethyl ether. The combined organic extracts were dried over Na2SO4, filtered and concentrated to afford 12.7 g (96%) of ethyl 4-cyanomethyl-2-piperidinecarboxylate. GC analysis showed an 85:15 mixture of cis:trans isomers. To a solution of 11.6 g (59.1 mmol) of the product in 60 ml of dimethylsulfoxide was added 9.9 g (118.2 mmol) of sodium bicarbonate and 5.7 ml (7.9 g, 65.0 mmol) of allyl bromide. After 1 hr at room temperature, another 1.1 ml portion of allyl bromide was added, and after another 2 hours at room temperature, the mixture was poured into 100 ml of water and 100 ml of brine and was extracted 5 times with 50 ml each of dichloromethane and once with 50 ml of diethyl ether. The combined organics were washed with 100 ml of water, then dried over Na2SO4, filtered and concentrated. The residue was purified by preparative HPLC to afford 8.6 g (62%) of ethyl cis-(±)-4-cyanomethyl-N-allyl-2-piperidinecarboxylate and 1.2 g (9%) of ethyl trans-(±)-4-cyanomethyl-N-allyl-2-piperidinecarboxylate, both of which were >99.9% one isomer by GC.

Provenance & Evidence