Spiro conjugated chains

Conformational rigidity and flexibility are two key features for the development of an efficient chiral catalyst. Ma and coworkers developed a new generation of chiral dinuclear phase-transfer catalysts 47 by connecting two structurally rigid BINOL-derived chiral N-spiro quaternary ammonium salts with a flexible linker [80]. These catalysts were proven to act via dual activation of both nucleophiles and electrophiles and to be very efficient catalysts for the conjugate addition of hindered nitroalkanes to enones. Notably, a completely reversed enantioselectivity could be easily switched with catalysts (S,S)-47a and (S,S)-47b, which differ in the length of the methylene chain of the linker but not in the chiral element of backbone. 

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