Theoretical Studies On Syn-dichlorination Of Alkenes Catalyzed By Organoselenium And C-C Coupling Reaction Caalyzed By Iridium

Diphenyl selenide PhSeSePh,as the pre-catalyst,can be oxidized by oxidant and chlorine source to PhSeCl3 as the real catalyst in the system.We performed DFT method to investigate the reaction of syn-dichlorination of alkenes catalyzed by PhSeCl3 and PhSeCl.The calculation results indicate that PhSeCl3 is determined to be the active catalyst versus PhSeCl.Iridium catalyst[Ir(cod)Cl]2 is modified by chiral ligand(R)-H8-BINAP to obtain the chiral iridium catalyst Ir[(R)-H8-BINAP]I.Ir[(R)-H8-BINAP]I is used to catalyze the C-C coupling reaction of propargyl ether with alcohol,which is an important organic synthetic method.In this paper,we explored catalytic reaction mechanism catalyzed by organoselenium catalyst and chiral iridium catalyst using DFT calculation from the micro perspective on molecular level.The main research contents and valuable innovations in this dissertation are listed as follows:1.A new method of the syn-dichlorination of alkenes has been proposed by Denmark et al.using diselenide PhSeSePh as pre-catalyst at room temperature.Benzyltriethylammonium chloride(BnEt3NCl)is the chloride source and an N-fluoropyridinium salt is the oxidant to recover the catalyst.A number of alkene substrates have been syn-dichloridnated with exquisite diastereocontrol.In this paper,we perform DFT calculations to study the reaction mechanism by identifying a reasonable reaction path including the intermediate and transition state structures.In addition,PhSeCl3 is determined to be the active catalyst versus PhSeCl.We investigate the reaction mechanism of the syn-dichlorination of alkenes catalyzed by PhSeCl3.The reaction can be divided into three steps:the first step is PhSeCl3 loses a chloride ion to yield a strong electrophile PhSeCl2+,which is from the plane below coordinated to the C=C double bond to form the seleniranium ion imtermediate as the initial point.The first chloride ion attacks one carbon atom from the opposite side of Se to open the C-C-Se three-membered ring,and yields the(?-chloroalkyl)phenylselenium dichloride species IM2.The second chloride ion also attacks the other carbon atom from the opposite side of Se and displaces it as PhSeCl2-,which(dissociates to PhSeCl and Cl-first)can be oxidized to reproduce PhSeCl3,and thus completes the catalytic cycle.Denmark also assumed the addition of PhSeCl to the alkene could precede the oxidation of Se(II)to Se(IV).The first elementary reaction is also the nucleophilic attachment of chloride anion to the double bond carbon atom to open the C-C-Se ring.Our computational results show that the Gibbs free energy barrier of Path 1(13.9 kcal/mol)is much lower than Path 2(38.2 kcal/mol),indicating that the catalysis by PhSeCl3 is much favorable with that by PhSeCl.The NBO charge analysis explains the vast difference in reaction barrier,and can help with the design of more effective catalyst.2.Addition reaction of ?,?-unsaturated carbonyl compounds is one of the most widely used method to build C-C bond.A novel method that C-C coupling of propargyl ether with alcohol via redox-triggered and highly enantioselective homoaldol addition was found.An unprecedented 1,2-hydride shift mechanism of propargyl ether provide clear evidence that convert to ?-allyls by deuterium labeling studies.Based on the theoretical calculation,C-C coupling reaction in turn by:1,2-hyride shift,HI protonation,tautomerism,C-C coupling of terminal olefins with aldehyde,exchanges hydrogen between alcohol and IM8,regeneration of iridium catalyst,the resulting configuration is(Z)-R-3b.Among the six steps,determined affecting factors of stereoselectivity and enantioselectivity of product 3b are the configure of C4 carbon center of aldehyde and relative location of two hydrogen atoms in IM6(IM6'),respectively.