Abstract:We have developed a gold affinity index and hydrogen bonding basicity index for counterions and have used these indexes to forecast their reactivity in cationic gold catalysis.
“…In these cases, the ability of a counterion to mediate the proton transfer (hydrogen bonding basicity) may play an important role. Indeed, in our previous investigation on the counterion effects on the gold-catalyzed reaction, we found that this was indeed the case ( Lu et al., 2017 ). Scheme 5 A Transition State Involves an Active Proton Transfer …”
Summary
Ionic reactions are the most common reactions used in chemical synthesis. In relatively low dielectric constant solvents (e.g., dichloromethane, toluene), ions usually exist as ion pairs. Despite the importance of counterions, a quantitative description of how the paired 'counterion' affects the reaction kinetic is still elusive. We introduce a general and quantitative model, namely transition-state expansion (TSE), that describes how the size of a counterion affects the transition-state structure and the kinetics of an ionic reaction. This model could rationalize the counterion effects in nucleophilic substitutions and gold-catalyzed enyne cycloisomerizations.
“…In these cases, the ability of a counterion to mediate the proton transfer (hydrogen bonding basicity) may play an important role. Indeed, in our previous investigation on the counterion effects on the gold-catalyzed reaction, we found that this was indeed the case ( Lu et al., 2017 ). Scheme 5 A Transition State Involves an Active Proton Transfer …”
Summary
Ionic reactions are the most common reactions used in chemical synthesis. In relatively low dielectric constant solvents (e.g., dichloromethane, toluene), ions usually exist as ion pairs. Despite the importance of counterions, a quantitative description of how the paired 'counterion' affects the reaction kinetic is still elusive. We introduce a general and quantitative model, namely transition-state expansion (TSE), that describes how the size of a counterion affects the transition-state structure and the kinetics of an ionic reaction. This model could rationalize the counterion effects in nucleophilic substitutions and gold-catalyzed enyne cycloisomerizations.
“…Screening of different mixtures of solvents as well as of different alkene to diazonium ratios showed that the reaction performed best with a mixture of 4% MeOH in toluene using 1.5 equivalents of the alkene (see Tables 1 and 2 in Supporting Information). Addition of just 5 mol% of the cationic reaction promoter KCTf 3 substantially increased the reaction yield from 63% to 77% (entries 1 and 2 from Table ) …”
Enantioselective substrate directed Heck reactions are desirable for the stereoselective synthesis of complex molecules. However, due to the coordination requirements of both chiral ligands and directing groups, such methodologies are underdeveloped. We report herein the desymmetrization of meso (1R,2S)cyclohex-4-ene-1,2-diol in an enantioselective and substrate directed fashion. The method provides all cis substituted highly functionalized chiral allylic alcohols in a complementary fashion to other Heck protocols.The products were obtained in high enantioselectivities (higher than 95% ee) and moderate to high yields (38-87%). The noncovalent interactions responsible for the directing effect were elucidated through computational examination of relevant minima and transition structures.
“…The cationic Au I catalyst in each case was prepared in situ from equimolar quantities of the appropriate ligated AuCl and silver(I) triflimide that were delivered as standard solutions in dichloromethane . A significantly faster reaction was observed in the case of the triphenylphosphino complex (entry 1), but under identical conditions the yield of 4 was better with the aryl phosphite ligand (entry 3), so it was chosen . Since there was no significant difference between 1,2‐dichloroethane and dichloromethane (entries 3, 4) dichloromethane was selected .…”
The cationic AuI‐catalyzed cyclization of highly substituted enynes has been shown to provide cyclopentenones with up to two contiguous, all‐carbon atom quaternary centers in a diastereospecific process. In the more challenging examples in which two contiguous quaternary centers are formed during cyclization, the essential role of a ethoxycarbonyl group to control the reaction outcome has been demonstrated. The less challenging examples that lead to a single quaternary center in the ring require no activation by aryl or by electron withdrawing groups.
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