Stereoselective Generation of Cis or Trans Olefins from the RuCl2(PPh3)3-Catalyzed Diazo Coupling of Ethyldiazoacetate

The RuCl2(PPh3)3-catalyzed diazo coupling of ethyl diazoacetate was manipulated to generate either diethyl fumarate (DEF) or diethyl maleate (DEM) with high stereoselectivity. A mechanism was proposed which contained separate pathways for DEM and DEF formation and explained how reaction conditions were controlled to favor either pathway.