Methanol → D-Proline

Participants

Reaction Conditions

Reaction Steps

N-(L-menthoxyacetyl)-2-pyrroline is prepared by condensation of 0.1 mol of 2-pyrroline with 0.1 mol of L-menthoxyacetyl chloride. A 70 mL stainless steel high pressure reactor fitted with a Pyrex glass liner and magnetic stir bar is charged with THF (5 mL), methanol (0.5 mmol), Co2 (CO)8 (0.05 mmol), pyridine (0.25 mmol), and N-(L-menthoxyacetyl)-2-pyrroline (0.5 mmol.) The reactor is sealed, pressurized to 1000 psig with CO, and the reaction mixture is stirred for 24 hours at 100° C. The product mixture, isolated after removal of gas from the reactor vessel, contains a mixture of N-(L-menthoxyacetyl)-D-proline methyl ester and N-(L-menthoxyacetyl)-L-proline methyl ester. Separation of these products is effected by silica gel chromatography with ether-toluene eluent, and the diastereomers are treated separately with 2N HCl solution at 100° C. for 3 hours to give pure L-proline and D-proline.

Provenance & Evidence