Highly enantioselective [4+2] annulation via organocatalytic Mannich-reductive cyclization: one-pot synthesis of functionalized piperidines.

A new method for one-pot synthesis of 2,3-substituted piperidine from N-PMP aldimine and aqueous glutaraldehyde via formal [4+2] cycloaddition is reported. This reaction involves organocatalytic direct Mannich reaction-reductive cyclization with high yields (up to 90%) and excellent enantioselectivities (up to >99%). The practicability of this method is also shown at a gram scale as well as through the synthesis of functionalized (-)-anabasine.