Formal Aza-Diels--Alder Reactions of Spiroindolenines with Electronrich Dienes.

Spiroindolenines were employed as cyclic imine substrates in formal aza-Diels--Alder reactions with Danishefsky's diene or silyloxy-substituted electron-rich dienes for the synthesis of the corresponding tetrahydropyrido[1,2-α]spiroindolinones. The reactions occur under mild conditions in the presence of ytterbium triflate as Lewis acidic catalyst delivering the desired compounds in good yield. The reaction results in the preparation of a small library of a new class of conformational constrained heterocyclic derivatives that easily undergo selective and efficient manipulations. [ABSTRACT FROM AUTHOR]