ps as well.In conclusion, the Lu (3 + 2) cycloaddition has been investigatedwith joint forces putation and experiment. The formation ofa 1,3-dipole is slightly exothermic, and the subsequent (3 + 2)cycloaddition is a stepwise process with an activation free energyof 28.3 kcal/mol. The generally accepted intramolecular [1,2] protonshift in the Lu reaction is not possible owing to the very high activation barrier of 39.6 kcal/mol required for this process.Calculations and experiments revealed that water assists this process with an activation free energy of 7.7 kcal/mol. The discovery of the catalytic role of a trace amount of water in the Lu reaction suggests that a trace amount of water could also act as a catalyst in some other “anhydrous” reactions involving [1,2] or [1,n] proton shifts.
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