Organocatalytic Stereoselective Addition of Aldehydes to Acylquinolinium Ions

A direct and simple activation of quinolines, without isolating unstable intermediates, or using isolated N,O-acetals in the presence of Lewis or Brønsted acids, is described. The procedure is quite straightforward and allows the addition in a stereoselective manner of different aldehydes to various differently substituted quinolines. The desired products were obtained in 28–76 % yields, with dr values up to 83:17 in favor of the syn isomer, and up to 99 % ee. Studies towards the use of acetaldehyde were also performed with different catalysts and the addition was promoted affording the desired product in 62 % yield with 46 % ee. Finally, deprotection and chemical transformations of the enantioenriched adducts were performed.