Reductive amination with secondary amines
Methyl iodide, CH3I ) will result in significant formation of the undesired tertiary amine (i.e.
"Lehninger, Principles of Biochemistry" 3rd.The equilibrium between aldehyde/ketone and imine can be shifted toward imine formation by removal of the formed water through physical or chemical means.Only in the case of dicyclohexyl-amine the use of 1,4-dioxane gave better results thanthe use of a completely aqueous medium (entry 5).Barluenga,.; Bayon,.Direct treatment of benzylamine with an alkylating agent (e.g.In summary, the described procedure allows the selectivepreparation of mono- or dimethylated amines and aminoacids.These include sodium cyanoborohydride (NaBH3CN) and sodium triacetoxyborohydride (NaBH(ococh3)3).For example, look at the synthesis of the tertiary amine below.
Recent studies on the zinc promoted aminomethylationof alkyl halides,6 the formation of N-methylated tertiaryamines as side products in some cases prompted us toexplore this process for the simple, general, and selectiveN-methylation of primary and secondary amines.
There are two other commonly used reductants for reductive amination: sodium cyanoborohydride (NaBH3CN) and sodium tri-acetoxyborohydride (NaBH(OAc)3 ).Therefore we cant work backwards to compote materne bon de reduction the reduction of a CN bond with a hydride source.3, therefore, this suggests that in some cases the reaction proceeds via direct reduction of the hemiaminal species.However, when the dimethylation ofprimary amines or monomethylation of secondaryamines is desired, aqueous formaldehyde is an ecientand cheap methylating agent.The initial step entails formation of an imine, but the hydride equivalents are supplied by a reduced pyridine to give an aldimine, which hydrolyzes to the amine.It is connected to three carbons, which we can label a, b, and.Employing a ketone will result in a branched alkyl substituent on the amine.Yes, you could try and separate out the secondary amine thats formed from the tertiary amine, but were not going to settle for 10-30 yields here.The carbonyl group is most commonly a ketone or an aldehyde.Reductive amination is extremely versatile and can be used to install a large variety of different alkyl groups on an amine.A classic named reaction is the Mignonac Reaction (1921) 5 involving reaction of a ketone with ammonia over a nickel catalyst for example in a synthesis of 1-phenylethylamine starting from acetophenone : 6 In industry, tertiary amines such as triethylamine and diisopropylethylamine are formed directly.Its very helpful to be able to think backwards from an amine product to what the starting materials look like.Tel.: ; fax: ; e-mail: 'H, CH2 R'.This is a much more controlled manner of forming nitrogen-carbon bonds.