Clean and Simple Chemoselective Reduction of Imines to Amines Using Boric Acid-Activated Sodium Borohydride under Solvent-Free Conditions

Abstract

The first clean and highly effective solvent-free chemoselective reduction of functionalized aldimines and ketimines bearing easily reducible functional groups, such as ketone, carboxylic acid, ester, nitrile, amide, nitro, furyl and alkenyl groups, to the corresponding amines using boric acid-activated sodium borohydride is described.The reduction of aldimines and ketimines to the corresponding amines is a very useful transformation in organic synthesis because of their versatile utility as intermediates for synthesis of pharmaceuticals 1 and agrochemicals. 2 As effective reducing methods for these conversions, catalytic hydrogenation, 3 metal hydride reductions using NaBH

Reductive amination of aldehydes and ketones by NaBH4using carbon-based solid acid (CBSA) as catalyst

“…For these conversions, hydrogen can be produced as reducing agent in the presence of metal catalysts (4Á8), ZnÁAcOH (9), Et 3 SiHÁCF 3 CO 2 H (10), Bu 3 SnHÁ DMF (11), NaBH 4 along with catalysts such as various acids (12), boric acid/p-toulenesulfonic acid/ benzoic acid (13), boric acid (14), acetic acid (15), trifluoroacetic acid (16), silica-phosphoric acid (17), iodine (18), indium chloride (19), guanidine-hydrochloride (20), 12-tungstophosphoric acid (21), ionic liquids (22), titanium (IV) isopropoxide (23), and polyaniline salt (PANI) (24). In addition, there are some reports on development of electrochemical reductive amination reactions (25Á27).…”

Organic Solid-State Reactions

“…1 : 1 : 1 molar ratios of the components were ground in a mortar with pestle for 40 min to yield 98% of the amine after extractive isolation. The technique was applied to several solid or liquid aldimines and ketimines by actually kneading grinding [99]. It should, however, be tested whether or not milling as in the above cases of aldehydes and ketones at proper temperatures can use all of the four hydrogens of NaBH 4 , if in the presence of solid acids as catalysts.…”

Synthesis of Novel Chalcones as Acetylcholinesterase Inhibitors

“…Ten benzylaminochalcones derivatives (A1-A10) with different substituents on ring B were prepared as shown in Scheme 1 [21][22][23][24][25]. The 1-(4-((2-Hydroxybenzyl)amino)phenyl)-ethanone 1 and benzaldehyde derivatives (in proportion of 1:1) were dissolved in methanol with stirring.…”