Reduction of benzylic alcohols and α-hydroxycarbonyl compounds by hydriodic acid in a biphasic reaction medium

Abstract

SummaryThe synthetic protocol for the reduction of alcohols to hydrocarbons by using hydriodic acid, first described by Kiliani more than 140 years ago, was improved to be more applicable to organic synthesis. Instead of a strongly acidic, aqueous solution, a biphasic toluene–water reaction medium was used, which allowed the conversion of primary, secondary and tertiary benzylic alcohols, in good yields and short reaction times, into the corresponding hydrocarbons. Red phosphorous was used as the stoichiometric reducing agent. Keto, ester, amide or ether groups are tolerated, and catalytic amounts of hydriodic acid (0.2 equiv) in the presence of 0.6 equiv phosphorous are sufficient to achieve conversion.

Reductive Deoxygenation of Alcohols: Catalytic Methods Beyond Barton–McCombie Deoxygenation

“…They regenerated hydroiodic acid either by chemical reduction with H 3 PO 3 or by electrochemical reduction, [73] but the harsh conditions of these methods are still problematic for use in organic synthesis. [74] Cleavage of methyl ethers and dehalogenation reactions were not observed with this protocol in contrast to the classic method. [74] Cleavage of methyl ethers and dehalogenation reactions were not observed with this protocol in contrast to the classic method.…”

“…Scheme 31. König et al described the use of red phosphorus and catalytic amounts of aqueous HI in biphasic reaction media for the reduction of benzylic alcohols (Scheme 32). [74] P red = red phosphorus. Scheme 32.…”

An efficient and metal free synthesis of benzylpyridines using HI through the deoxygenation reaction

“…This result clearly shows that second aryl group is necessary for deoxygenation reaction. 15 If the R group is hydrogen or aliphatic group, exclusively it gives acetylated product 13 where as if the R group is aromatic, then the reaction gives exclusively deoxygenated product 12. Both aryl and heteroaryl secondary alcohols underwent for this Scheme 1 Synthesis of 2-benzylpyridines.…”

“…To nd out the synthetic utility of this acetoxylation reaction, various alkyl substituted substrates were subjected for this transformation and the results are summarized in Table 5. 15,16 On the other hand, when the starting material is arylmethanol or arylalkylmethanol, it may give acetylated product 13 via simple S N 2 displacement by acetic acid due to mono benzylic nature of substrate may not generate the stable radical for deoxygenation. acetoxylation reaction in the presence of hydroiodic acid and gave excellent yield.…”

A study on the synthesis of β-amino acids: the first synthesis of a bicyclic hemiaminal (3,3-dimethyl-1-(2,4,5-trifluorophenyl) tetrahydro-3H,5H-oxazolo[3,4-c] [1,3] oxazin-5-one)

“…For practical reasons, the diastereomeric alcohols 7 were not isolated but directly subjected to a further reaction. The reduction of the benzylic OH group was carried out by various methods [22]. One of these methods was direct Pd/C catalyzed hydrogenation of benzylic ketones or alcohols.…”