Reductive amination in case of secondary amines

When an aldehyde or a ketone undergoes reductive amination when a primary amine is acting,the mechanism follows a pathway through hemiaminal and imine,what happens when a secondary amine is acting on the given carbonyl ? There will be no hydrogen on the amine nitrogen in this case to facilitate loss of water with the hydroxyl group of the hemiaminal.How does the reaction proceed then?

• Secondary amines undergo reductive amination perfectly well via the iminium ion. This explains it clearly chemistryscore.com/reactions/reductive-amination – Waylander Jul 25 '19 at 12:35
• Did you read @Waylander's link? The mechanism is there. – user55119 Jul 25 '19 at 14:34
• Yes I did , actually I was not able to follow the answer there , what I was able to gather from there was that the reducing agent , LiAlH4 in my case , will substitute the OH and nitrogen will grab a hydrogen from water – Aditya Prakash Jul 25 '19 at 14:37
• Sodiumtriacetoxyborohydride in DCM is my reagent of choice for reductive aminations. LiAlH4 will just reduce your ketone before it reacts with the amine – Waylander Jul 25 '19 at 15:06

In modern organic synthesis, reductive amination of aldehydes and ketones is considered one of the important and principal ways to make secondary and tertiary amines. It is a powerful and reliable strategy for the formation of $$\ce{C–N}$$ bonds. One of the advantages of the reductive amination is it can avoid the problem of over-alkylation that is always the problem with direct alkylation of amines with alkyl halides.
Most common condition is sodium triacetoxyborohydride ($$\ce{NaB(OAc)3H}$$) in THF or dichloroethane (DCE) under slighly acidic conditions (common acid used is acetic acid)(Ref.1).