RESUMO
A novel iminium ion cascade reaction has been developed that allows for the stereoselective synthesis of a variety of substituted aza-fused bicycles. The combination of amino allylsilanes and aldehydes (or ketones) was used to synthesize a number of quinolizidines and indolizidines in an one-pot reaction sequence. This technology has been used to effect the facile syntheses of several indolizidine and quinolizidine natural products including, (±)-epilupinine, (±)-tashiromine, and (-)-epimyrtine. Substrate scope has been examined varying the type of amino allylsilanes (primary, secondary and conjugated) and carbonyl compounds (aldehydes and ketones) to give a variety of fused ring structures. Varying the components chosen allows for the inclusion of synthetically useful functional groups at different positions on the core structure. The methodology has been used to construct the tricyclic core structures present in the cylindricine family and halichlorine.
RESUMO
Several novel cascade processes have been designed and developed that involve sequential reactions of imines and iminium ions to form substituted quinolizidine ring systems in a single step from simple and readily available starting materials. The utility and promise of these cascade reactions is evident from their application to extraordinarily concise syntheses of the representative quinolizidine alkaloids (+/-)-epilupinine and (-)-epimyrtine.
