Diastereoselective Mannich-Based Synthesis of Piperidones

Significance

Reported is the diastereoselective synthesis of 3,4,5-substituted piperidones by a Lewis acid mediated Mannich reaction of aminol ethers with β-keto esters. The α-methyl β-keto ­esters shown were used as starting materials as the use of α,α-unsubstituted β-keto esters led only to the formation of high molecular weight polymeric material. It is of some surprise that this simple reaction appears not to have been previously reported.