- 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
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(Chemical Equation Presented) A triruthenium cluster, (μ3, η2,η3,η5-acenaphthylene)Ru 3(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.
- Hanada, Shiori,Ishida, Toshiki,Motoyama, Yukihiro,Nagashima, Hideo
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p. 7551 - 7559
(2008/02/12)
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- Hydride Transfer Reaction Products in the Aminomethylation of Styrene
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Aminomethylation of styrene with formaldehyde and dimethylamine leads to N-methylbenzenepropanamine (1), N-(3-phenylpropyl)benzenepropanamine (3), and α-methylenebenzenepropanal (4) as major products.The ratio of 1, 3 and 4 is considerably influenced by the ratio of the reactants.The best yield of 1 is obtained by using dimethylamine in excess.Styrene in excess favors the formation of 3, and equivalent amounts of reactants afford the best yield of 4.Using formaldehyde in excess leads to the complete N-methylation of 1 and 3.When styrene reacts with formaldehyde and diethylamine or diisopropylamine the most important aminomethylation products are N-ethylbenzenepropanamine (11) or N-isopropylbenzenepropanamine (12), respectively, and 3 and 4 in both cases.The formation of the major products in the aminomethylation of styrene can be explained by the hydride transfer mechanism represented earlier as one competing mechanism for the aminomethylation of certain bicyclic alkenes.The N-methylation of amine 1 and 3, when formaldehyde is used in excess, is due to Eschweiler methylation under aminomethylation conditions.
- Manninen, Kalle,Karjalainen, Aira
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p. 190 - 195
(2007/10/02)
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