Amino Acids. 7. A Novel Synthetic Route to L-Proline

Article abstract of DOI:10.1021/jo00368a019

Reaction of L-5-oxoproline esters L-2 with phosgene at 0 deg C gives L-5,5-dichloro-1-(chlorocarbonyl)proline esters L-6, which readily lose hydrogen chloride to form L-5-chloro-1-(chlorocarbonyl)-4,5-dehydroproline esters L-7.Catalytic hydrogenation (Pd/C, 180 bar) of L-7 yields L-1-(chlorocarbonyl)proline esters L-15 and thence, upon hydrolysis, L-proline (L-17).A 'one-pot reaction' for the whole sequence is described, starting from easily accessible L-5-oxoproline esters and yielding L-proline in 78percent overall yield and 99.7percent optical purity.