D. A. Evans Sigmatropic Rearrangements: An Overview Chem 206 [1, 2] Sigmatropic Rearrangements: Carbon The Wittig Rearrangement [1, 2] [2, 3]-Wittig Sigmatropic Rearrangements in Organic Synthesis. " Nakai, [1, 2]sigmatropic rearrangements to cationic centers allowed T: Mikami, K. Chem. Rev. 1986. 86, 885 agner-Meerwein Rearrangemer Marshall, J. A. The Wittig Rearrangement. Trost, B. M. and Fleming, I Ed. Pergamon Press: Oxford, 1991; Vol. 3, pp 975 8-9 BuLi consider as cycloaddition Ea-16 Kcal/ mol FMO anal R This 1, 2-sigmatropic non-concerted R olefin radical cation transition state The Wittig Rearrangement [2, 3] R [ 2]-Sigmatropic rearr to carbanionic centers not observed concerted R FMO analysis consider as cycloaddition FMO analysis ketyl radical 六 olefin radical anion transition state Allyl radical The aagt between concerted and non-concerted pathways can be quite small● ● ● R R R R R R R R O R C O O R R H BuLi O R Li O Li C O OLi R R H O Li R D. A. Evans Sigmatropic Rearrangements: An Overview Chem 206 [1,2] Sigmatropic Rearrangements: Carbon + + consider as cycloaddition transition state ● ● olefin radical cation ● + [1,2]-Sigmatropic rearrangements to cationic centers allowed. Wagner-Meerwein Rearrangement [1,2]-Sigmatropic rearr to carbanionic centers not observed consider as cycloaddition ●● ●● stepwise ● olefin radical anion ●● ● ●● ● antibonding transition state The Wittig Rearrangement [1,2] "[2,3]-Wittig Sigmatropic Rearrangements in Organic Synthesis.", Nakai, T.; Mikami, K. Chem. Rev. 1986, 86, 885. Marshall, J. A. The Wittig Rearrangement.; Trost, B. M. and Fleming, I., Ed.; Pergamon Press: Oxford, 1991; Vol. 3, pp 975. ● R● This 1,2-sigmatropic rearrangement is non-concerted The Wittig Rearrangement [2,3] Allyl radical ketyl radical ●● ●● Ea ~16 Kcal/mol The G ‡ between concerted and non-concerted pathways can be quite small ●● concerted transition state FMO analysis FMO analysis FMO analysis