Fig. 6: Mechanistic studies for enantioselective propargylic alkylation.

a Formation of the ruthenium–allenylidene complex in the presence of BF3·Et2O. b Stoichiometric reaction of the ruthenium–allenylidene complex with 4-alkyl-dihyropyridine. c Ruthenium–allenylidene complex-catalyzed reaction. d Reaction in the presence of TEMPO.