title: Mechanistic Insights into the Cu(I)- and Cu(II)-Catalyzed Cyclization of o-Alkynylbenzaldehydes: The Solvent DMF and Oxidation State of Copper Affect the Reaction Mechanism.
abstract: A computational study with the BhandHLYP density functional is conducted to elucidate the mechanisms of Cu(I)- and Cu(II)-catalyzed reactions of o-alkynylbenzaldehydes with a nucleophile (MeOH). Our calculations suggest the following. (a) The use of CuCl as a catalyst deceases significantly the energy barrier and promotes intramolecular cyclization. (b) Solvent DMF is critical in the stepwise hydrogen-transport process involved in an intermolecular nucleophilic addition because it can greatly reduce the free energy barrier of the hydrogen-transfer process as a proton shuttle. In addition, we find that substrate MeOH also plays a role similar to that of DMF in the hydrogen-transport reaction. (c) The 6-endo product P1 is formed exclusively using a catalytic system consisting of CuCl and DMF, whereas a mixture of 6-endo product P1 and 5-exo product P2 in a ratio of ∼1:1 is produced using CuCl2 and DMF as a catalytic system. Our theoretical calculations reproduce the experimental results very well. This study is expected to improve our understanding of Cu(I)- and Cu(II)-catalyzed reactions involving Lewis base solvents and to provide guidance for the future design of new catalysts and new reactions.
authors.affiliation: Key Laboratory of Luminescence and Real-Time Analytical chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
authors.forename: Binfang
authors.initials: B
authors.lastname: Yuan
authors.affiliation: Key Laboratory of Luminescence and Real-Time Analytical chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
authors.forename: Rongxing
authors.initials: R
authors.lastname: He
authors.affiliation: Key Laboratory of Luminescence and Real-Time Analytical chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Shen
authors.affiliation: Key Laboratory of Luminescence and Real-Time Analytical chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Huang
authors.affiliation: Key Laboratory of Luminescence and Real-Time Analytical chemistry (Southwest University), Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
authors.forename: Ming
authors.initials: M
authors.lastname: Li