An Easy Approach to Obtain Alcohol-Amines by Reduction of Alcohol Functionalized Imines

Abstract

The reduction of functionalized imines to yield amines is often an intricate task, since most of the methods described in the literature to reduce imines to amines do not take into account that many reducing agents have also basic character. In this way, iminic compounds that have phenol functions usually produce the phenolic salt of the precursor when they are treated with a basic reducing agent, but not the desired amine. In this work, we describe an easy way of isolating very pure aminic compounds with alcoholic functions in its structure from the corresponding iminic compounds, by using NaBH4 as a reducing agent, and avoiding tedious chromatography or multiple solvent extraction steps.

Asymmetric Henry Reaction of Nitromethane with Substituted Aldehydes Catalyzed by Novel In Situ Generated Chiral Bis(β-Amino Alcohol-Cu(OAc)2·H2O Complex

“…Previously asymmetric Henry reaction has been reported by Lu et.al. [59] with very good yield (89-98% ee) in 24-48 h at 10 °C, using similar type of amino alcohol chiral ligand-Cu(OAc)2•H2O. Jin et.al.…”

“…Although, higher enantioselectivities (81-94% ee) and yields (82-99%) were found corresponding to the ortho, meta, para nitro-benzaldehyde, p-tolualdehyde and benzaldehyde (Table 4, entry 1-3, 11, 13), However, there is no clear, conclusive evidence which suggests that there is any kind of influence in the enantioselectivity due to steric factor as well as electronic environments of the substituents in the aromatic ring (Table 4, entries 1-13). Previously asymmetric Henry reaction has been reported by Lu et al [59] with very good yield (89-98% ee) in 24-48 h at 10 • C, using similar type of amino alcohol chiral ligand-Cu(OAc) 2 •H 2 O. Jin et al reported asymmetric Henry reaction with excellent enantiomeric excess using CuBr-diamine catalyst in the presence of another additive like pyridine [40]. Amino Alcohol-Cu(II) complex has been used to catalyze asymmetric Henry reaction by Qin et al and very high ee % obtained with prolonged time 48-72 h. However, in our study we have optimized the reaction at room temperature in ethanol as green solvent, good to high enantiomeric access were achieved without using any additives within reasonable timeframe (24-48 h) at ambient temperature.…”

“…4a-e) in methanol under reflux for 24 h afforded the corresponding enamines (4a-e) those were successfully reduced by NaBH 4 (2.6 eq.) [59], in ethanol to yield the desired chiral bis (β-amino alcohol) ligands (L1-L5) in 65-75% isolated yield and excellent optical purity (Scheme 1). All the intermediates (2, 3, 5a-e) and final ligands (L1-L5) were characterized by NMR, LCMS and FT-IR techniques.…”

“…Several Literature suggest that the retention time of the R enantiomer is lesser than the S enantiomer for the nitroaldol products. Therefore, the absolute configuration of all the newly synthesized chiral nitroaldol product (8a-m) were assigned as R respectively by comparing their retention time found in reported literature [40,59,61,62]. Scheme 5.…”

“…The chiral enamines (5a-e) (1 mmol) suspended in dry ethanol (20 mL) followed by portion wise addition of NaBH 4 (2.6 eq.) in four equal parts and kept on stirring at ambient temperature for 24 h [59].…”