TiCl4-promoted cyclization reactions of aminoacetals and ethenetricarboxylates leading to nitrogen-containing heterocycles.

Lewis acid-catalyzed cyclization of aminoacetals 2 and triethyl ethenetricarboxylate (1a) has been examined. The reaction of 3-aminopropionaldehyde diethyl acetal (2a) and 1a in the presence of 1 equiv of TiCl(4) at room temperature gave 4-ethoxypiperidine-2,3,3-tricarboxylate 3a in 92% yield with a 2,4-diastereomer ratio of 1:1. The reaction in the presence of 3 equiv of TiCl(4) gave 2,4-trans-piperidine derivative 3a in 86% yield predominantly. The reaction of aminoacetaldehyde diethyl/dimethyl acetals 2c,d and 1a with 3 equiv of TiCl(4) gave 2,4-trans-4-pyrrolidine-2,3,3-tricarboxylates 5a,b predominantly.