Annulations of enantioenriched allenylsilanes with in situ generated iminium ions: stereoselective synthesis of diverse heterocycles.

Highly enantioenriched allenylsilanes participate in Lewis acid mediated annulations with in situ generated iminium ions derived from tert-butyl carbamate and methyl carbamate to selectively form functionalized 4,5-dihydropyrroles and 4,5-dihyrooxazines, respectively. The dihydropyrrole products were further elaborated in a stereocontrolled vinylsilane terminated cyclization with in situ generated oxonium ions, resulting in pyranopyrroles.