The Ruthenium-Catalyzed Reduction and Reductive N-Alkylation of Secondary Amides with Hydrosilanes:  Practical Synthesis of Secondary and Tertiary Amines by Judicious Choice of Hydrosilanes

Shiori Hanada, Toshiki Ishida, Yukihiro Motoyama, and Hideo Nagashima*
Institute for Materials Chemistry and Engineering, Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
J. Org. Chem., 2007, 72 (20), pp 7551–7559
DOI: 10.1021/jo070591c
Publication Date (Web): August 31, 2007
Copyright © 2007 American Chemical Society

Abstract

Abstract Image

A triruthenium cluster, (μ3235-acenaphthylene)Ru3(CO)7 (1) catalyzes the reaction of secondary amides with hydrosilanes, yielding a mixture of secondary amines, tertiary amines, and silyl enamines. Production of secondary amines with complete selectivity is achieved by the use of higher concentration of the catalyst (3 mol %) and the use of bifunctional hydrosilanes such as 1,1,3,3-tetramethyldisiloxane. Acidic workup of the reaction mixture affords the corresponding ammonium salts, which can be treated with a base, providing a facile method for isolation of secondary amines with high purity. In contrast, tertiary amines are formed with high selectivity by using lower concentration of the catalyst (1 mol %) and polymeric hydrosiloxanes (PMHS) as reducing agent. Reduction with PMHS encapsulates the ruthenium catalyst and organic byproducts to the insoluble silicone resin. The two reaction manifolds are applicable to various secondary amides and are practical in that the procedures provide the desired secondary or tertiary amine as a single product. The product contaminated with only minimal amounts of ruthenium and silicon residues. On the basis of the products and observed side products as well as NMR studies a mechanistic scenario for the reaction is also described.

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History

  • Published In Issue September 28, 2007
  • Received March 28, 2007

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