Solid-Phase Synthesis of Chiral Silicon-Based Reagents and Their Application to Organic Synthesis

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New synthetic intermediates and reagents for organic synthesis have been developed in response to the demands for the efficient construction of large chemical libraries consisting of optically active organic molecules. The results of this research projects are summarized below.(1)Polymer-bound optically active allylsilanes were synthesized via palladium-catalyzed solid-phase intramolecular bis-silylation of optically active allylic alcohols. Thus obtained allylsilanes were found to react with electrophiles, giving highly enantioenriched alcohols and cyclic ethers stereoselectively.(2)Silylboranes react with various unsaturated organic molecules including vinylcyclopropane and terminal allenes, leading to the synthesis of new organic molecules that contain silicon and boron. Enantioface-selective silaboration of terminal allenes has been developed by using chiral phosphine ligands with palladium complexes, affording enantio-enriched 2-borylallysilanes efficiently, which serve as new 2-b … More orylallyllation reagents for the synthesis of functionalized organoboron compounds.(3)Cyanoboranes were found to add to carbon-carbon triple bonds in the presence of palladium catalysts. The reaction provides a unique access to 2-borlyacrylonitriles, which serves as convenient reagents for the synthesis of highly substituted α,β-unsaturated nitriles.(4)Aminoboranes serve as new iminium ion generators in organic synthesis. The reagent allows to avoid acidic reaction conditions, which are usually required for the amination reactions that proceed via the formation of iminium ion intermediates. Strecker reaction, Mannich reaction and reductive amination reactions proceed in the presence of aldehydes, nucleophiles, and aminoboranes under non-acidic reaction conditions.(5)As a related research project, a new screw-sense selective polymerization reaction has been developed Polymerrization of 1,2-diisocyanobenzen derivatives proceeded with optically active arylpalladium(II) complexes, leading to the formation of optically active poly(quinoxaline-2,3-diyl)s. The selectivity reaches >90% screw-sense excesses when structurally well-tuned chiral organopalladium initiators were used. Less