Palladium-Catalyzed Asymmetric Ring Expansion of Allenylcyclobutanols:  An Asymmetric Wagner−Meerwein Shift

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In this study, we developed a palladium-catalyzed atom economic asymmetric Wagner-Meerwein shift of allenylcyclobutanol substrates. It is an excellent method for creating functionalized cyclopentanones with an alpha-chiral O-tertiary center by ring expansion of allenylcyclobutanols. This reaction was initiated by hydropalladation and afforded excellent enantioselectivity as well as atom economy. This method provides an efficient route toward the synthesis of natural products such as trans-kumausyne's family, spiro ring systems. In addition, we obtained excellent diastereoselectivity and enantioselectivity at the same time by using 3-monosubstituted allenylcyclobutanol.