I have moiety that having Boc protected amine as well as free amine and I want to prepare the shciff base of that free amine grp with formaldehyde?
Reaction does not proceeding to completion, i can not use here acidic condition as it may lead to boc deprotection. I also tried to use basic condition but reaction not going to completion...so suggest me suitable reaction condition..
Formaldehyde is too reactive and so are the imines formed with it. Most methaneimines will either give cyclic trimers or undergo further transformations. Actually, I can't remember any example of stable methaneimine, regardless of the substituent at nitrogen. May be you should try other aldehyde. Also, don't be too wary about the Boc-group - it can survive mildly acidic conditions.
I agree with Dr. Angelov, aliphatic imines especially methaneimines are usually less stable. However, you can try the reaction with the help of a mild Lewis acid. This may not interfere with the Boc group.
All the best
for inspiration see using non-Brønsted acid catalyst :https://www.researchgate.net/publication/267390365_Comparative_Studies_of_Catalytic_Application_of_Cerium%28III%29_Chloride_and_Resin_Supported_Cerium%28III%29_in_Domino_Syntheses_of_15-Benzodiazepine_and_13-Diazine_Skeletons
or
https://www.researchgate.net/publication/265959505_Synergism_of_Metal_and_Organocatalysis_in_Condensation_Reactions_of_Aromatic_Aldehydes_with_Anilines_Affording_Imines_Effect_of_Catalysts_on_the_Base_of_a_Supported_Cerium%28III%29_and_Proline
Article Comparative Studies of Catalytic Application of Cerium(III) ...
Article Synergism of Metal and Organocatalysis in Condensation React...
In addition to Dr Angelov's comments, I would add that N-Boc is stable in the presence of weak acids such as acetic acid, which has been used in reductive aminations (Abdel-Magid et al) to promote mine formation. However as mentioned, your issue maybe the very reactive formaldehyde.
Dear all thanks for our reply...but my methaneimine is acid and water sensative. I am successful to prepare compound having methaneimine (schiff base with formaldehyde) and boc protected amine functionality in same compound.Now my target is to deprotect that Boc group...but that methanimine functionality is sensitive to water as well as acid hence i am not getting suitable condition to deBoc the compound....I would like to well come your additional suggestion if any...
Have you tried removing the Boc group in anhydrous conditions e.g. HCl in diethyl ether or dioxane (both commercially available) or TFA/DCM (1:1). It may be that your methanimine maybe more stable to acidic conditions in anhydrous conditions.
What do you do with the methanimine next? Can this be done prior to Boc deportation. The problem you are likely to face is that the methanimine is probably always going to be the most reactive part of the molecule. Because of this you with need to react it on in the next step, or experiment with mild/quick deportations that are less likely to expose the methanimine to reactive conditions. With the HCl/diethyl ether method, you may find that your product precipitates out rapidly as the HCl salt after Boc deprotection which means it will not be sitting in the acidic reaction environment.
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