Peer-reviewed literature and organic chemistry textbooks confirm that carboxylic acids can be efficiently reduced to alcohols using various forms of borane and borane complexes.
The present work prepared a copper N‐heterocyclic carbene complex that could be used in catalyzing the homogeneous hydrogenation of carboxylic acid with ammonia borane (hydrogen source) to synthesize primary alcohols. Various aromatic and aliphatic carboxylic acids with diverse functional groups were transformed to respective alcohols in moderate to high yields. The process can be easily scaled up (TON up to 14545) and exhibits a high compatibility with different sensitive functional groups, including fluorine, chlorine, bromine, iodine, hydroxyl, cyano and nitro groups. IMesCuCl/NH3·BH3 combination can selectively reduce aromatic and aliphatic esters. Mechanistic studies indicate that Cu‐H species produced in situ are the active intermediates.
Abstract Doxyl2 (4,4-dimethyloxazolidine-N-oxy1) nitroxides and the more recently introduced proxyl3 (for example, 8) nitroxides are important stable free radicals for the study of biological systems using the spin labeling technique.4 Chemical transformations on molecules already bearing a nitroxide grouping lead to new nitroxide spin labels, providing of course, that the synthetic steps do not destroy the somewhat sensitive nitroxide grouping.4 We wish to report that nitroxide carboxylic acids can be smoothly reduced to the corresponding nitroxide alcohols in high yield using borane methyl sulfide5 in ether solution at 25°C. Heretofore, LiAlH4 has been employed for this reduction.6 Since borane methyl sulfide and LiAlH4 differ considerably in their reactivity toward other functional groups5, the borane methyl sulfide reagent constitutes a valuable alternative to LiAlH4 for chemically modifying nitroxide carboxylic acids which also bear other functional groups susceptible toward reduction by LiAlH4.
We report a general protocol for the reduction of different kinds of carboxylic acids to produce alcohols using a commercial heterogeneous Pd‐catalyst and ammonia borane as a reducing agent. Applying this Pd‐based catalyst, a series of aromatic, heterocyclic, and aliphatic carboxylic acids, including di‐acids, were reduced to their corresponding alcohols in good to excellent yields. Interestingly, fatty acids were also conveniently converted to fatty alcohols with a yield of up to 98%. Further, the synthetic utility of this reduction process is showcased by performing late‐stage reduction of bioactive compounds.
"Synthesis of Borane-Ammonia and its Application in the Titanium Tetrachloride Catalyzed Reduction of Carboxylic Acids, Including N-Protected Amino Acids". Org
Ammonia borane (also systematically named ammonio(trihydrido)borate), also called borazane, is the chemical compound with the formula H3NBH3. The colourless or white solid is the simplest molecular boron-nitrogen-hydride compound. It has been investigated as a storage medium for hydrogen fuel, but is otherwise primarily of academic interest.
(NH4)2SO4 + 2 NaBH4 → BH3·NH3 + Na2SO4 + 2 H2
The initially formed ammonium borohydride [NH4]+[BH4]− is unstable and dehydrogenates under ambient conditions to form ammonia borane. These processes are generally higher…
REDUCTION OF CARBOXYLIC ACIDS The carboxylic group in carboxylic acids can be reduced to an aldehyde … Reduction of Carboxylic Acids 139 Reduction of Aromatic Carboxylic Acids Aromatic carboxylic acids can be reduced … Alcohols Reduction with Borane Reduction of Carboxylic Acids to Alebhols Reduction with Borane in situ Reduction
REDUCTION OF CARBOXYLIC ACIDS The carboxylic group in carboxylic acids can be reduced to an aldehyde … Reduction with Borane 209 Reduction of Carboxylic Acids to Alcohols 20. Reduction with Borane in … even polynuclear aromatics and carboxylic acids can be reduced to saturated hydrocarbons but
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