Highly Regio- and Stereoselective Three-Component Nickel-Catalyzed syn-Hydrocarboxylation of Alkynes with Diethyl Zinc and Carbon Dioxide

摘要

Activation of carbon dioxide and converting it into useful chemical feedstock have attracted much attention owing to the fact that CO2 is abundant, inexpensive, nontoxic, and environmentally benign. However, the challenges still to be overcome are its lack of thermodynamic and kinetic stability. For the reaction of allylic tin species, aryl boronates, and limited examples of 1-alkenyl boronates, aryl or alkyl zinc substrates can react with carbon dioxide, usually under palladium, nickel, copper, or rhodium catalysis [Scheme 1, Eq. (1)]. In addition, a stoichiometric amount of Ni or Ti reagents have been used to mediate the reaction of CO2 with alkene, diene, alkyne,or allene substrates to form five-membered metallaoxacyclic intermediates A, which may undergo further reactions to afford carboxylation products [Scheme 1, Eq. (2)]. There are very limited reports on the catalytic reactions of alkyneor allene substrates involving A-type intermediate using 20mol% of [Ni(cod)2] and 10 equivalents of l,8-diazabicyclo[5.4.0]undec-7-ene.