Rh(?)-Catalyzed Enantioselective Cyclopropenation Of Internal Alkynes With 1-Phenylsulfonyl-1,1-difluorodiazoethane

Enantioenriched cyclopropenes,the smallest carbocycles,have high ring strain energies with versatile reactivity and significant research value.The[2+1]-cycloaddition reaction with terminal alkyne has witnessed substantial advances.In sharp contrast,the extension of this chemistry to disubstituted internal alkynes has proved extremely challenging,mainly due to the attenuated reactivity and difficult stereocontrol associated with increased steric hindrance.This dissertation described an efficient Rh^II-catalyzed enantioselective cyclopropenation reaction of internal alkynes with a masked difluorodiazoethane reagent(Ph SO₂CF₂CHN₂,Ps-DFA).This asymmetric transformation offers efficient access to a broad range of enantioenriched difluoromethylated cyclopropenes(40examples,up to 99%yield,97%ee).The synthetic utility of obtained strained carbocycles is demonstrated by subsequent stereodefined processes,including cross-couplings,hydrogenation,Diels–Alder reaction and Pauson–Khand reaction.