Synthesis of 2‐carboxy‐4‐methylazetidine. A novel isomeric analog of dl ‐proline

L‐Azetidine‐2‐carboxylic acid is a naturally occurring azetidine currently used in the synthesis of abnormally high molecular weight polypeptides. The synthesis of 2‐carboxy‐4‐methylazetidine is now reported which is a novel isomeric analog of dl‐proline. Reaction of α,β‐dibromo carbonyl ester with three molar equivalents of benzylamine yields 1‐benzyl‐2‐carbomethoxy‐4‐methyl‐azetidine. Hydrolysis of the latter compound with barium hydroxide yields 1‐benzyl‐2‐carboxyl‐4‐methylazetidine which, if subjected to catalytic hydrogenation., yields the title compound in practical yield. The cis configuration is tentatively assigned to the title compound on the basis of previously published arguments.