Tandem intramolecular silylformylation and silicon-assisted cross-coupling reactions. synthesis of geometrically defined alpha,beta-unsaturated aldehydes |
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Authors: | Denmark Scott E Kobayashi Tetsuya |
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Institution: | Department of Chemistry, Roger Adams Laboratory, University of Illinois, Urbana, Illinois 61801, USA. denmark@scs.uiuc.edu |
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Abstract: | The palladium- and copper-catalyzed cross-coupling reactions of cyclic silyl ethers with aryl iodides are reported. Silyl ethers 3 were readily prepared by intramolecular silylformylation of homopropargyl silyl ethers 2 under a carbon monoxide atmosphere. The reaction of cyclic silyl ethers 3with various aryl iodides 7 in the presence of (allyl)PdCl](2), CuI, a hydrosilane, and KF.2H(2)O in DMF at room temperature provided the alpha,beta-unsaturated aldehyde coupling products 8 in high yields. The need for copper in this process suggested that transmetalation from silicon to copper is an important step in the mechanism. Although siloxane 3 and the product 8 are not stable under basic conditions, KF.2H(2)O provided the appropriate balance of reactivity toward silicon and reduced basicity. The addition of a hydrosilane to (allyl)PdCl](2) was needed to reduce the palladium(II) to the active palladium(0) form. |
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