Mechanistic studies of the (DHQD)2PHAL catalyzed asymmetric chlorolactonizationreaction of alkenoic acids have led to some surprising conclusions. Deuterium labelingstudies of the catalyzed reaction have revealed that the face selectivity of the delivery ofthe chlorenium ion to olefins is neither a necessary nor a sufficient condition to deliverthe product lactones with high enantioselectivities. The reaction likely proceeds via acarbocation intermediate with the enantioselectivity originating as a result of "templation"of the cyclization of the acid nucleophile by the chiral catalyst. Reaction progress kineticanalysis (RPKA) competition studies revealed that the rate-determining step is theformation of the chloronium ion. Taken together, these results suggest that the ratedetermining step and the enantioselectivity determining step are segregated. Moreover,NMR studies lead us to a plausible resting state of the asymmetric chlorolactonization.
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