A Heterocycle-Forming Double Michael Reaction. [5 + 1] Annulation Route to Highly Substituted and Functionalized Piperidines

[reaction: see text]. Nitrogen-containing tethered diacids, easily prepared by reductive alkylation of diethyl aminomalonate or ethyl cyanoglycinate, undergo double Michael reactions with 3-butyn-2-one to give highly functionalized and substituted piperidines (pipecolic acid derivatives) with surprisingly high stereoselectivity. The heterocyclic double Michael adducts can be induced to undergo further cyclizations to give a variety of azabicyclic and diazabicyclic compounds.