A concise highly enantioselective cascade synthesis of indolizidine alkaloids with a quaternary stereocenter

Enantiomericallypure indolizidinones bearing a quaternarystereocenter were obtained by Rh(II)-catalyzed decomposition of a-diazo ketodiesters through a carbenoid/spiro[5,5]ammonium ylide/Stevens [1,2]-shift with a ring-expansion cascade process. The isolation of stable chiral ammonium ylides, namely the key intermediates of the process, unambiguously confirmed the stereochemistryof the total process