The first catalytic asymmetric [3+2] allylsilane annulation for the synthesis of cyclopentanes is described. Using alkylidene oxindole electrophiles, the reaction generates a quaternary spirocenter with up to 97% yield, and excellent diastereo- and enantioselectivity (up to 99:1 dr, 99:1 er). The enantioselective annulation is catalyzed using a scandium(III)-indapybox complex with sodium tetrakis-[3,5-bis(trifluoro-methyl)phenyl]-borate (BArF) as an essential additive for catalytic activity and stereoselectivity. Trapping of the �-silyl carbocation by formation of a lactone product is described. The effect of various catalysts on lactone formation is examined. Mechanistic insight into the catalyst complex and the role of NaBArF using 1H, 19F and 45Sc NMR spectroscopy is presented.

Sc-catalyzed enantioselective cyclopentane annulations with allylsilanes

248th National Meeting (2014)

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