Construction of 4a,8a-cis-octahydroquinolin-7-one core using an intramolecular aldol type of cyclization: An application to enantioselective total synthesis of lepadin B

An intramolecular aldol type of cyclization of the piperidine derivative 1 proceeded in highly stereoselective manner to afford the desired 4a,8a-cis- octahydroquinolin-7-one. This key step involves a feature of the use of A((1.3)) strain as a control element, in biasing 1 towards the conformer desired for the above cyclization. An application of this aldol reaction to enantioselective total synthesis of the marine alkaloid lepadin B is also described.