(Stranger / Eraser)
Aldehydes from carboxylic acids
(Rated as: excellent)
nice work from Chemical Communications without using complex hydrides:
New Pd-catalyzed selective reduction of carboxylic acids to aldehydes
A catalyst generated in situ from palladium acetate and tricyclohexylphosphine efficiently catalyzes the reduction of carboxylic acids with sodium hypophosphite in the presence of pivalic anhydride to give aldehydes with high selectivity. The low cost and convenient handling of the reagents makes this process a valuable alternative to hydrogenations and metal hydride reductions.
Synthesis of 4-acetamidobenzaldehyde (3h): A 100 mL flask was charged with 4-acetamidobenzoic acid (1h) (1.79 g, 10.0 mmol), potassium phosphate (2.12 g, 10.0 mmol) and sodium hypophosphite monohydrate (1.59 g, 15.0 mmol). The reaction vessel was purged with argon and degassed THF (50 mL) was added. Then, a solution of palladium acetate (67.3 mg, 0.30 mmol) and tri-cyclohexylphosphine (196 mg, 0.70 mmol) in THF (10 ml), pivalic anhydride (4.65 g, 25 mmol) and finally water (1 mL) were added by syringe and the reaction mixture was stirred at 60 °C overnight. After removal of the volatiles in vacuo, the residue was filtered through silica gel using hexane–MTBE (MTBE = tert-butyl methyl ether) gradient as eluent. The compound was eluted with 50% MTBE in hexane. After removal of the volatiles and crystallization of the residue from hexane, 4-acetamidobenzaldehyde 3h (1.14 g, 69 %) was obtained as colorless crystals.
Chem.Comm. 2002, 836-837
|There was an old method of using the calcium salt ...||Bookmark|
There was an old method of using the calcium salt of a benzoic acid with calcium formate to obtain the corresponding aldehyde, also the Rosemund or somthing reduction effectively did the same thing with the corresponding acid chloride of the carboxylic acid. Does this seem to use less exotic compounds? Quite interesting though