Synthesis of nitrogen heterocycles via the intramolecular [4+2] cycloaddition of iminoacetonitriles

Abstract

Iminoacetonitriles have been shown to function as aza dienophiles in intramolecular Diels-Alder reactions, affording substituted quinolizidines and indolizidines. The cycloadducts are formed with a high preference for an exo-orientated cyano group due to the a-amino nitrile anomeric effect. The substrates for these [4+2] cycloadditions are prepared from readily available alcohols via a Mitsunobu reaction with the previously unknown N-cyanomethyltriflamide (HN(Tf)CH₂CN) followed by cesium carbonate promoted elimination of trifluoromethanesulfinate. The a-amino nitrile cycloadducts are versatile synthetic intermediates and can be elaborated via alkylation, reduction, and nucleophilic addition chemistry to provide a variety of substituted and functionalized nitrogen heterocycles. Initial investigations have been undertaken to explore the use of this methodology in the total synthesis of alkaloid natural products.