A convenient electrolytic process for the reduction of aldehydes

Figures & data

Scheme 1. Synthesis and reduction of 2-aryl imidazo[1,2-a]azines-3-carbaldehyde 3 and 4. Reaction conditions: (a) N₂, anh DMF/POCl₃/0–100°C, 1 h then aq. KOH, (b) ethyl alcohol, NaBH₄/0.1 N NaOH/rt, then 0.1 N HCL, and (c) electrochemical reduction, copper electrodes, H₂O/electric current, e^-/rt

Table 1. Yields of 2-aryl-3-hydroxymethyl imidazo[1,2-a]pyridines 5 by reduction with NaBH₄ and by electrolysis of corresponding 2-aryl imidazo[1,2-a]pyridine-3-carbaldehyde 3.

Compound 5	Reduction process yield (%)		Voltage	Melting point (°C)
R	NaBH4	Electrolysis	VS	Experimental	Literature [14]
H	70	80	0.75	202–203	>212
Cl	61.3	95	0.91	229–230	>240
F	70.3	80	0.96	154–155	153–155
Me	76.7	85.7	0.12	274–275	>290
MeO	66.7	95	0.45	166–167	165–167
3,4-diMeO	70.9	87.5	0.63	171–172	170–172
NO2	70.0	80	0.12	225–226	224–226

V_S, solution voltage.

Table 2. Yields of 2-aryl-3-hydroxymethyl imidazo[1,2-a]pyrimidines 6 by reduction with NaBH₄ and by electrolysis of corresponding 2-aryl imidazo[1,2-a]pyrimidine-3-carbaldehyde 4.

Compound 6	Reduction process yield (%)		Voltage	Melting point (°C)
R	NaBH4	Electrolysis	VS	Experimental
H	60.6	83.3	0.16	241–242
Cl	63.8	88.9	0.46	164–165
F	30.3	80	0.1	232–233
Me	32	91.6	1.10	199–200
MeO	86	90.9	0.11	187–188
3,4-diMeO	30.4	90	0.6	200–201
NO2	72	83.3	0.14	213–214

V_S, solution voltage.

Scheme 2. Other aldehydes reduced by electrolysis.

Table 3. Synthesis of primary alcohols from diverse aldehydes by electrolysis.

Aldehyde	VS	Alcohol	Yield%	Melting point (°C)	Boiling point (°C)
2-Nitrobenzaldehyde	0.60	2-Nitrobenzyl alcohol	90	70–72
Salicylaldehyde	0.61	Salicyl alcohol	91	84–87
Butyraldehyde	1.30	Butanol	90		117–118
3-Nitrobenzaldehyde	0.01	3-Nitrobenzyl alcohol	91	30–31
Benzaldehyde	0.20	Benzyl alcohol	90		205–206
4-Fluorobenzaldehyde	0.05	4-Fluorobenzyl alcohol	90		208–209
4-Methylbenzaldehyde	1.0	4-Methylbenzyl alcohol	91	56–61
4-Formylbenzonitrile	1.70	4-Cyanobenzyl alcohol	90	39–40
4-Methoxybenzaldehyde	0.48	4-Methoxybenzyl alcohol	90	22–23
4-Chlorobenzaldehyde	0.50	4-Chlorobenzyl alcohol	90	69–70
4-Hydroxybenzaldehyde	0.65	4-Hydroxybenzyl alcohol	90	116–118
Furfural	0.05	Furfuryl alcohol	90		170
3-Methoxy-4-hydroxy benzaldehyde	1.54	3-Methoxy-4-hydroxybenzyl alcohol	91	110–111

V_S, solution voltage.

Scheme 3. Synthesis and attempted electrolytic reduction of 2-arylimidazo[2,1-b]thiazole-3-carbaldehyde derivatives.

Scheme 4. Electrosynthesis of 2-aryl-3-hydroxymethyl imidazo[1,2-a]azines.