Palladium(II)-Catalyzed Allylic Rearrangement

Among the numerous transition metal catalysts, Palladium possess extremelyimportant status. Recently, palladium(Ⅱ)－catalyzed reaction has been widely studiedfor its high selectivity, environmental friendship, atomic economy, etc. In this paper,Palladium(Ⅱ)－catalyzed allylic rearrangement reaction is described. And the contentincludes mainly three aspects as follows:Firstly, palladium(Ⅱ)－catalyzed allylic rearrangement reaction, in which a seriesof allylic N－tosyl carbamates were used as the substrates, has been deeply studied.To optimize the reaction conditions, the main factors are widely discussed and thesubstrates were extended. The results are as follows: Conditions will be stricter if thestructure is more complicated; The amount of catalyst doesn't impact the reactionvery much; Halide salt is necessary and should be excessive; Base doesn't impact thereaction; THF, 1,4－dioxane, DMF as preferred solvents fit different reactivetemperatures. Besides, cyclized byproduct was discovered beyond our imagination.Secondly, the applications of this methodology were extended to many otherkinds of substrates, such as (1) allylic carbamate, (2) N－Cbz or (3) N－Boc allyliccarbamate. It indicated that substrate (1) couldn't be rearranged. However, substrates(2) and (3) obtained the rearranged products as expectation.Based on the previous work and proposed mechanisms according to somereferences, the tendencious mechanism was chosen, and the formation mechanism ofthe cyclized byproduct was also explored.Finally, this methodology was extended to N－Tosyl cyclopropylmethylcarbamates rearrangement reseach. But because of the unstability of the startingmaterial, the rearranged product couldn't be obtained. In addition, another kind oftransition metal－rhodium was also tried and obtained some good results.