title: Mechanistic insights on DBU catalyzed β-amination of nbs to chalcone driving by water: Multiple roles of water.
abstract: DFT calculations were conducted to pursue deeper understandings on the mechanism and the explicit role of trace water in the DBU-catalyzed β-amination of NBS to chalcone. Being different from previously proposed by Liang et al., a cooperative participation of both DBU and water is noticed in the preferred mechanism. The preferential mechanistic scenario assisted by water undergoes three major steps: the formation of succinimide and HBrO, concerted nucleophilic addition and H-shift, and keto-enol tautomerization. Moreover, we found that DBU-HBrO is unnecessary in the third step and three-water-cluster assisted keto-enol tautomerization is the most advantageous case. It is further noted that the catalytic position of the third water molecule and the proton shift orientation to some extent affect step 3 via O···HO and OH···π interactions, which is confirmed by AIM analysis. The computational results suggest that water molecules play pivotal roles as reactant, catalyst, and stabilizer to promote the reaction of chalcone and NBS. The origin of the more stable transition state structure in the rate-determining step of DBU-water catalyzed mechanism is ascribed to noncovalent interactions, halogen bond, and electrostatic interactions than DBU only ones. © 2017 Wiley Periodicals, Inc.
authors.affiliation: Jilin Province Key Laboratory of Organic Functional Molecular Design & Synthesis, Advanced Energy Materials Research Center, Faculty of Chemistry, Northeast Normal University, Renmin Street 5268#, Changchun, 130024, China.
authors.forename: Haiyan
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Jilin Province Key Laboratory of Organic Functional Molecular Design & Synthesis, Advanced Energy Materials Research Center, Faculty of Chemistry, Northeast Normal University, Renmin Street 5268#, Changchun, 130024, China.
authors.forename: Jingping
authors.initials: J
authors.lastname: Zhang
keywords: DBU; density functional theory; mechanism; water; β-amination of chalcone