Rosenmund reduction acyl chlorides

The Pd-catalyzed hydrogenoiysis of acyl chlorides with hydrogen to give aldehydes is called the Rosenmund reduction. Rosenmund reduction catalyzed by supported Pd is explained by the formation of an acylpalladium complex and its hydrogenolysis[744]. Aldehydes can be obtained using other hydrides. For example, the Pd-catalyzed reaction of acyl halides with tin hydride gives aldehydes[745]. This is the tin Form of Rosenmund reduction. Aldehydes are i ormed by the reaction of the thio esters 873 with hydrosilanes[746,747]. 

The reduction of acyl halides with hydrogen to form aldehydes using Pd catalyst is well known as the Rosenmund reduction[756]. Some acyl chlorides give decarbonyiation products rather than aldehydes under Rosenmund conditions. The diene 890 was obtained by decarbonyiation in an attempted Rosenmund reduction of acetyloleanolic acid chloride (889)[757], Rosenmund reduction of sterically hindered acyl chlorides such as diphenyl- and tnpheny-lacetyl chloride (891) gives the decarbonylated products 892[758],... 

The acylpalladium complex formed from acyl halides undergoes intramolecular alkene insertion. 2,5-Hexadienoyl chloride (894) is converted into phenol in its attempted Rosenmund reduction[759]. The reaction is explained by the oxidative addition, intramolecular alkene insertion to generate 895, and / -elimination. Chloroformate will be a useful compound for the preparation of a, /3-unsaturated esters if its oxidative addition and alkene insertion are possible. An intramolecular version is known, namely homoallylic chloroformates are converted into a-methylene-7-butyrolactones in moderate yields[760]. As another example, the homoallylic chloroformamide 896 is converted into the q-methylene- -butyrolactams 897 and 898[761]. An intermolecular version of alkene insertion into acyl chlorides is known only with bridgehead acid chlorides. Adamantanecarbonyl chloride (899) reacts with acrylonitrile to give the unsaturated ketone 900[762],... 

The name Rosenmund reduction is used for the catalytic hydrogenation of an acyl chloride 1 to yield an aldehyde 2. 

The Rosenmund reduction is usually applied for the conversion of a carboxylic acid into the corresponding aldehyde via the acyl chloride. Alternatively a carboxylic acid may be reduced with lithium aluminum hydride to the alcohol, which in turn may then be oxidized to the aldehyde. Both routes require the preparation of an intermediate product and each route may have its advantages over the other, depending on substrate structure. 

Acyl chloride (acid chloride) is hydrogenated over catalyst, palladium on barium sulphate. This reaction is called Rosenmund reduction. 

A variation of the Rosenmund reduction is heating of an acyl chloride at 50° with an equivalent of triethylsilane in the presence of 10% palladium on charcoal. Yields of aldehydes obtained by this method ranged from 45% to 75% [80]. 

Reduction of acid chlorides to aldehydes One of the most useful synthetic transformations in organic synthesis is the conversion of an acid chloride to the corresponding aldehyde without over-reduction to the alcohol. Until recently, this type of selective reduction was difficult to accomplish and was most frequently effected by catalytic hydrogenation (the Rosenmund reduction section 6.4.1). However, in the past few years, several novel reducing agents have been developed to accomplish the desired transformation. Among the reagents that are available for the partial reduction of acyl chlorides to aldehydes are bis(triphenylphosphine)cuprous borohydride , sodium or lithium tri-terf-butoxyaluminium hydride, complex copper cyanotrihydridoborate salts °, anionic iron carbonyl complexes and tri-n-butyltin hydride in the presence of tetrakis(triphenylphosphine)palladium(0). ... 

Table 3 Yields and Conditions for Selected Classical Rosenmund Reductions of Acyl Chlorides RCOCl with...

The mechanism of the Rosenmund reduction has attracted occasional attention. The discovery of Tsuji et al that palladium metal can catalyze the conversion of acyl chlorides (11) into alkenes (13), carbon monoxide and HCl, presumably via intermediates of the form (12 Scheme 5), suggests that (12) may also be an intermediate in the Rosenmund reaction. Consistent with this suggestion is the observation that the unsaturated acyl chloride (14) is converted to phenol by a palladium catalyst.22... 

Catalytic hydrogenation is often chosen as a method for reduction because of its chemoselectivity for C=C double bonds and benzylic C-X bonds over C=0 groups. The most important hydrogenation involving a carbonyl compound is not actually a reduction of the C=0 double bond. Hydrogenation of acyl chlorides gives aldehydes in a reaction known as the Rosenmund reaction—really a hydrogenolysis of a C-Cl bond. 

Rosenmund reduction of the corresponding acyl chloride (Refs 2 3)... 

Tsuji, J., Ono, K., Kajimoto, T. Organic syntheses with noble metal compounds. XX. Decarbonylation of acyl chloride and aldehyde catalyzed by palladium and its relation with the Rosenmund reduction. Tetrahedron Lett. 1965, 4565-4568. 

Rosenmund reduction The reduction of an acyl chloride to an aldehyde by hydrogenation using a palladium on barium sulphate catalyst. 

ROSENMUND SAITZEW Reduction to Aldehyde Hydrogenation of acyl chlorides to aldehydes in the presence of poisoned Pd catalyst. 

The reduction of an acyl chloride can be stopped at an aldehyde if a partially deactivated catalyst is used. This reaction is known as the Rosenmund reduction. The catalyst for the Rosenmund reduction is similar to the partially deactivated palladium catalyst used to stop the reduction of an alkyne at a cis alkene (Section 6.8). 

This reaction was initially reported by Reissert in 1905 and extended by Grosheintz and Fischer in 1941 It is the synthesis of aldehyde involving the formation of 1 -acyl-2-cyano-1,2-dihydroquinoline derivatives from acyl chlorides, quinoline, and potassium cyanide and the subsequent hydrolysis of said dihydroquinoline derivatives under acidic conditions to produce quinaldic acid and aldehydes. The original procedure occurs smoothly for aroyl or cinnamoyl chloride in liquid SO2 but not in benzonitrile, ether, dioxane, acetone, or CHCb. However, the modification from Grosheintz and Fischer using hydrogen cyanide and 2 eq. quinoline in absolute benzene is also adaptable for aliphatic acid chlorides. This is one of the methods that converts acyl chlorides into aldehydes and is found to be superior to the normal Rosenmund Reduction. For example, o-nitrobenzoyl chloride has been converted into o-nitrobenzaldehyde in 60% yield by the current reaction, whereas the Rosenmund Reduction is not suitable for such conversion. Therefore, this reaction is referred to as the Grosheintz-Fischer-Reissert aldehyde synthesis or Reissert aldehyde synthesis. ... 

The mechanism (Scheme 48) ° is expected to proceed through the acylpalladium species much as in the Rosenmund reduction. Indeed, the acyl complex 56 from oxidative addition of vinyl chloride with Pd(CO)(Ph3P)3 was isolated (Scheme 49). " The reaction of acid chlorides with the same catalyst provides aldehydes. However, aliphatic acid chlorides do not reduce effectively. The phosphine ligands present in the Heck acylpalladium intermediate are thought to be the cause, allowing decarbonylation and elimination to occur. Interestingly, the formylation will not occur with the Rosenmund catalyst. 

The acyl-alkyl rearrangement becomes a main path with some acyl halides. Actually, formation of the decarbonylation product has been reported in several cases as an abnormal reaction of the Rosenmund reduction. Sterically hindered acyl halides such as diphenylacetyl and triphenylacetyl chlorides and naphthoyl chloride undergo decarbonylation in attempted Rosenmund reduction (Scheme... 

Amino-3-methylpyridine (29) has been used for synthesis fluorine-containing pyridine aldoximes of potential use for the treatment of organophosphorus nerve-agent poisoning [30]. The Baltz-Schiemann technique was used to convert 2-amino-3-methylpyridine into 2-flnoro-3-methylpyridine (30), subsequent permanganate oxidation of 30 provided acid 31. Finally conversion of 31 to acyl chloride 32 and Rosenmund reduction resnlted in carboxaldehyde 33. Previously this technique was reported to give poor yields with heterocyclic acyl chlorides. The conversion of 32... 

Several reduction methods are available to convert nitriles (Stephen reaction) or acyl chlorides (Rosenmund reduction) or amides to aldehydes. The use of lithium aluminum hydride at low temperatures or lithium triethoxyaluminum hydride appears to be a more effective means of reduction than the stannous chloride-HCl used in the Stephen method or palladium and hydrogen used in the Rosenmund reduction. 

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