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Reductive amination using paraformaldehyde





N-heterocyclic carbene boranes (NHC-boranes) are among the most nucleophilic classes of neutral hydride donors.
Heres a concrete example.
The solvent can be revovered and reused.And the organic layer was separated.The organic layer was separated and the aqueous part was extracted once with dichloromethane (25 mL).Khaksar, Synthesis, 2011, 490-496.You could even say its crappy.A direct reductive amination of ketones using the Hantzsch ester in the presence of S -benzyl isothiouronium chloride as a recoverable organocatalyst converts a wide range of ketones as well as aryl amines to the expected products in good yields.Drying of the organic extracts and concentration provided N-methylated amines which were purified either by distillation or by flash chromatography.Lett., 2006, 8, 741-744.
Imino esters derived from aryl and alkyl keto esters could be reduced to the corresponding -amino esters in excellent yields and in high enantiomeric excesses using 5 mol- concours de la poste 2018 of a chiral phosphoric acid as catalyst, Hantzsch ester as hydride donor, and toluene as solvent.
How do you do it?
A simple and convenient procedure allows the reductive amination of aldehydes and ketones using sodium borohydride as reducing agent and boric acid, p -toluenesulfonic acid monohydrate or benzoic acid as activator under solvent-free conditions.
The very weak base m-nitroaniline (pka.47) was also converted into the corresponding N,N-dimethylated product in good yield.
Once the imine forms at pH 4-5, some of it will be converted into its conjugate acid, an iminium salt.
That would lead to lower yields.
Lett., 2007, 9, 267-270.The table below shows examples of how methyl, ethyl, propyl, butyl, and benzyl groups can be installed on an amine, by employing an appropriate aldehyde.Heres the mechanism for imine formation, cdg34 resultat concours agent de maitrise in case youve forgotten.While alkylation can happen multiple times on an amine, imines only form once on a given amine.The nice part is that the groups just go on once.Sodium borohydride (0.76 g, 20 mmol) was then added and the resulting mixture was stirred for.In the schemes below, well use NaBH3CN, but NaBH4 and NaBH(OAc)3 can be considered to work just as well.Dicyclohexylamine and diisopropylamine which might exhibit steric hindrance to N-substitution were smoothly converted into the corresponding N-methylated tertiary amines in nearly quantitative yields.You may recall that NaBH4 is used for the reduction of aldehydes and ketones.Cooperative catalysis of an Ir(III)-diamine complex and a chiral phosphoric acid or its conjugate base enables a direct reductive amination of a wide range of ketones.If a molecule contains both an amine and a carbonyl, then it can cyclize to give a cyclic amine.8, scheme, the utility of this method is evaluated by reacting a mixture of paraformaldehyde and various amines containing potentially acid-sensitive or reducible functional groups with zinc chloride and sodium borohydride.Zinc chloride has been found to be compatible with a variety of acid-sensitive functional groups including acetals.

It is connected to three carbons, which we can label a, b, and.
Heres a more versatile way to make amines that doesnt result in over-alkylation.
In the reductive amination of some aldehydes with primary amines where dialkylation is a problem, a stepwise procedure involving imine formation in MeOH followed by reduction with NaBH4 was developed.


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