Dear Colleagues,
Any suggestions for alternatives to cyanoborohydride (in respect of less toxic, cheaper, suitable for aqueous settings)?
It's about the reductive amination of a polysaccharide (hence the aqueous solvent). The amine is to be added in slight excess vs. aldehyde and the resulting imine (or better aldimine) then should be reduced selectively in order to stabiilze the adduct,
I thought about dithionite, but it seems to have considerably less (if at all) selectivity over imine vs. aldehyde.
I use sodium triacetoxyborohydride for most imine reductions in a variety of solvents. i.e. DMF, THF, DCM. If you can run the reaction in methanol then add some trimethylorthoformate to assist with imine formation.
http://pubs.acs.org/doi/abs/10.1021/jo960057x?journalCode=joceah
Check it....
For selective reduction of imines in the presence of aldehydes you can use sodium bis(methoxyethoxy)aluminium hydride in toluene, xylene, benzene at 0 °C (M. Hudlický in Reductions in Organic Chemistry, J. Wiley and Sns. 1984, p. 132.
http://en.wikipedia.org/wiki/Sodium_bis(2-methoxyethoxy)aluminumhydride
I use sodium triacetoxyborohydride for most imine reductions in a variety of solvents. i.e. DMF, THF, DCM. If you can run the reaction in methanol then add some trimethylorthoformate to assist with imine formation.
Commonly, I use the sodium triacetoxyborohydride for imine reduction in presence of aldehydes in dichloromethane.
http://www.beilstein-journals.org/bjoc/content/pdf/1860-5397-7-125.pdf
Check it
It seemed sodium triacetoxyborohydride is another option. However，this chemical is sensitive to water and cannot be used in aqueous system. You can use it in organic solvent, but not in aqueous solution.
This is very specific method. I hope it will surely reduce imine keeping aldehyde intact.
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