Intramolecular Conjugate Displacement: A General Route to Hexahydroquinolizines, Hexahydroindolizines, and Related [m,n,0]-Bicyclic Structures with Nitrogen at a Bridgehead

N-Protected amino aldehydes can be converted into allylic alcohols by the classical Morita-Baylis-Hillman reaction (cf. 2 --> 3) or by condensation with selenium-stabilized carbanions, followed by oxidation (cf. 2 --> 8 --> 3). The derived acetates undergo cyclization when the nitrogen protecting group is removed, affording [m,n,0]-bicyclic structures with nitrogen at a bridgehead (cf. 4 --> 5 --> 6). Formation of bicyclic structures via the reactions of Schemes 1 and 2 is general, and the stereochemistry of the starting amino aldehyde is preserved.