Ive recently carried out a reaction to form a one carbon primary alcohol by firstly conducting a lithium halogen exchange, followed by reaction with DMF. Finally I added NaBH4 to give me the methanol fragment on my molecule. Im having a little trouble with understanding the mechanism and why i dont just get a reductive amination instead.
My intial assumption was that I would kick out NMe2
to form the carbonyl and then do a standard NaBH4
reduction. However surely the NMe2
would then go on to react with the aldehyde to form an imine instead? I found this site which explains that the resulting lithium salt is stable until you do an aqueous work up:http://www.alsnotebook.com/formylation.html
However now I am wondering how the NaBH4
would go about reducing that species without the aqueous work up in between? Also when you do an aqueous work up to try and get the aldehyde why do you not just get a reductive amination with the HNMe2
or form an acetal?