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Mechanism and Selectivity of Cinchona Alkaloid Catalyzed [1,3]-Shifts of Allylic Trichloroacetimidates
journal contribution
posted on 2009-09-18, 00:00 authored by Nihan Çelebi-Ölçüm, Viktorya Aviyente, K. N. HoukDensity functional theory calculations were used to investigate the [3,3]- and [1,3]-shifts of O-allylic trichloroacetimidates in the presence of cinchona alkaloids. Thermal [1,3]- and [3,3]-rearrangements proceed through concerted pseudopericyclic transition states to give the corresponding rearranged products. [1,3]-Rearrangement is catalyzed via a double SN2′ mechanism in which syn addition of the nucleophile is exclusively preferred in both steps. The catalyzed mechanism is favored by a 6.3 kcal/mol free energy difference compared to the alternative [3,3]-rearrangement pathway. The fast-reacting enantiomer is predicted to be determined by the availability of the H-bonding interaction between the catalyst and the substrate.
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presenceCinchonaMechanismtheory calculations6.3alternativetrichloroacetimidateenergy differencemechanismavailabilityenantiomerpseudopericyclic transition statespathwaysyn additionShiftAllylic TrichloroacetimidatesDensitycinchona alkaloidscatalystRearrangementCatalyzednucleophilesubstrateAlkaloidshiftrearrangementSelectivityThermalSNinteractionkcal
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