| In order to advance the existing methodology of allylsilane-terminated cyclizations, a series of amino-allyl(bis)silanes was prepared for use as intermediates in route to cationic cyclizations terminated by the novel allyl(bis)silane nucleophile. This terminator was found to readily participate in the intramolecular trapping of activated imines and C-acylnitrilium ions providing highly substituted and functionally diverse pyrrolidines, piperidines and pyrrolines. These processes occurred not only in high chemical efficiency under mild conditions but with excellent levels of regioselectivity and substrate based stereocontrol.;As a result, this methodology was successfully applied to the stereoselective synthesis of biologically active isotropane alkaloids and the azapolycyclic core of the potent natural insecticide, stemofoline. These applications demonstrated the ability of the allyl(bis)silane terminator to engage in tandem silicon-directed cyclizations. Such reactivity was not possible with the silane terminators previously used by synthetic chemists. |
