Aroyl chlorides, decarbonylation

Substituted aroyl- and heteroaroyltrimethylsilanes (acylsilanes) are prepared by the coupling of an aroyl chloride with (Me3Si)2 without decarbonylation, and this chemistry is treated in Section 1.2[629], Under certain conditions, aroyl chlorides react with disilanes after decarbonylation. Thus the reaction of aroyl chlorides with disilane via decarbonylation is a good preparative method for aromatic silicon compounds. As an interesting application, trimel-litic anhydride chloride (764) reacts with dichlorotetramethyidisilane to afford 4-chlorodimethylsilylphthalic anhydride (765), which is converted into 766 and used for polymerization[630]. When the reaction is carried out in a non-polar solvent, biphthalic anhydride (767) is formed[631]. Benzylchlorodimethylsilane (768) is obtained by the coupling of benzyl chloride with dichlorotetramethyl-disilane[632,633]. 

Various organotin reagents react with acyl and aroyl halides under mild conditions without decarbonylation to give carbonyl compounds[390,39l]. Alkyl- or alkenyltin reagents react with acyl and aroyl chlorides to give ketones[548.733,734]. One example is the preparation of the a,/3-dnsaturated 7-keto esters 860 and 861, carried out under a CO atmosphere[735]. The reaction has been applied intramolecularly to the synthesis of the macrocyclic keto... 

Decarbonylative cross coupling of acyl halides.8 This unusual reaction is observed on coupling aroyl chlorides with alkyl(phenyl)acetyl chlorides in the pres-... 

A third method for the palladium-catalyzed arylation of ethylene involves aroyl chlorides as the source of the aryl group and is accompanied by decarbonylation (equation 178).629 [Pd(OAc)2]... 

Under certain conditions, aroyl chlorides are converted to arylsilanes by the reaction with disilanes. The oxidative addition of aroyl chloride and decarbonylation are followed by transmetallation and reductive elimination to give aryl silanes. Neat trimellitic anhydride acid chloride (377) reacts with dichlorotetramethyldisilane (376) at 145 °C to generate 378, which affords 4-chlorodimethylsilylphthalic anhydride (379) by reductive elimination. Finally it was converted to 380 and used for polyimide formation [185], Biphenyltetracarboxylic anhydride 381 is obtained at a higher... 

Significant developments have been reported in Heck-type alkylations of alkenes or alkynes. Several reports have addressed the lack of reactivity of aryl chlorides in their reactions with alkenes. Two approaches to this problem have met with success. In the first case, aroyl chlorides are used in place of aryl chlorides under the conditions of reaction, oxidative addition followed by decarbonylation occurs. With activated alkenes, good yields of... 

The reagent also decarbonylates aroyl chlorides to aryl chlorides (ArCOCl------- ... 

The reaction occurs at room temperature or in refluxing benzene or toluene and yields are generally in the range 65-90%. The reagent also decarbonylates aroyl chlorides to aryl chlorides (ArCOCl — ArCI) at relatively low temperatures. Acyl halides of type (1) are converted into olefins 13... 

Scheme 35. Pd-catalyzed biaryl coupling of aroyl chlorides with decarbonylation [128]...

Aroyl chlorides + alkynes. Both decarbonylative addition and dechlorinative sdoaddition have been observed in the Rh-catalyzed reactions. 

Although aryl halides and triflates are the most commonly used arylating agents, there are successful examples where both aroyl chlorides and arylsulfonyl chlorides have been employed. Pd-catalyzed decarbonylations and desulfonylations and subsequent Heck couplings are often conducted with trialkylamines such as A-ethylmorpholine as a base, but improved yields are reported in cases in which the tertiary amine is replaced by a mixture of potassium carbonate and benzyltrioctylammonium chloride. In Table 2 two examples are given (entries 17 and 18). ... 

Chlorides can be prepared under mild, essentially neutral, conditions from hydroxyl compounds with triphenylphosphine in CCI4 Also acid chlorides can be prepared by this method Ar. chlorides in particular can be obtained in high yield at relatively low temp, by decarbonylation of aroyl chlorides with chlorotris-(triphenylphosphine) rhodium 99%-Formic acid has been found to be an excellent medium for chloromethylations... 

Aroyl chlorides and aryl sulfonyl chlorides can also be employed as arylating agents under decarbonylative and desulfitative conditions respectively. Improved yields were reported by Dubbaka and Vogel [64] using Herrmann s palladacycle [63], arenesul-fonyl chlorides and bulky trioctylmethylammonium chloride under reflux conditions (Figure 3.11). 

As an alternative to the use of aryl halides as electrophiles, Miura and coworkers [59] employed aroyl chlorides in rhodium-catalysed decarbonylative Mizoroki-Heck-type... 

Aroyl chlorides undergo silylative decarbonylation to give arylsilanes by the reaction of disilanes. Oxidative addition of aroyl chlorides and decarbonylation are followed by transmetallation with disilane to generate (aryl)silylpalladium, and its reductive elimination gives arylsilanes. For example, neat trimellitic anhydride add chloride reacted with dichlorotetramethyldisilane at 145 °C to afford 4-(chlorodimethylsilyl)phthalic anhydride by decarbonylation and reductive elimination. Also, trimellitic anhydride add chloride was converted to biphenyltetracarboxylic anhydride at 165 °C in refluxing mesitylene by reaction of the disilane. Thus, decarbonylation-coupling of aroyl chlorides offers a good synthetic method of biaryls (Scheme 7). ... 

This ARCIS reaction proved useful in the synthesis of a series of stilbenes and butyl cinnamates. By contrast, [RhCl(cod)]2 with PPh, was found to catalyze the decarbonylative addition of aroyl chlorides onto terminal alkynes to afford the coiresponding vinyl chlorides [27b]. 

Ir-Catalyzed Reactions (Z)-Vinyl chlorides are obtained selectively by the iridium-catalyzed decarbonylative addition of aroyl chlorides to terminal alkynes, using RuPhos as a phosphine ligand in refluxing toluene (20h) (Scheme 22.22) [31]. 

Pd catalysts also promote the decarbonylative Mizoroki-Heck reactions of even poorly reactive p-nitrophenyl aryl carboxylates with olefins to give the vinyl arenes in good to excellent yields, along with CO and the corresponding phenols [40]. Mizoroki-Heck-type arylation of styrene and acrylate esters by use of aroyl chlorides can also be performed in the presence of PdCljlPhCN) / (PhCHjlBUjNCl as the catalytic system without adding base [41]. 

Reactions of aroyl chlorides with neat hexamethyldisilane at 110°C are effectively catalyzed by [(7/3-C3H5)PdCl]2with triethylphosphite to give benzoyltrimethylsilane in satisfactory yields (14—71%). Aryltrimethylsilanes are also formed in a few cases. This reaction is apphcable to a variety of ortho-, meta-, and /lara-substituted aroyl chlorides. Under these conditions, phenyl-glyoxalyl chloride produces benzoyltrimethylsilane as the sole product in 52% yield through a facile decarbonylation process. ... 

Iridium complexes have been shown to catalyse intermolecular additions of acid chlorides R COCl to terminal alkynes R C=CH producing (Z)- -chloro-a, -unsaturated ketones R C(Cl)=CHCOR. Ligands play a key role in this reaction NHC is efficient for the addition of aroyl chlorides, whereas dicyclohexyl(2-methylphenyl)phosphine (PCy2(o-Tol) is indispensable for the reaction of aliphatic acid chlorides. Among the salient features of these transformations is the suppression of decarbonylation and j6-hydrogen elimination. Some mechanistic insight has been obtained from stoichiometric experiments. ... 

Mesylates are used for Ni-catalysed reactions. Arenediazodium salts 2 are very reactive pseudohalides undergoing facile oxidative addition to Pd(0). They are more easily available than aryl iodides or triflates. Also, acyl (aroyl) halides 4 and aroyl anhydrides 5 behave as pseudohalides after decarbonylation under certain conditions. Sulfonyl chlorides 6 react with evolution of SO2. Allylic halides are reactive, but their reactions via 7t-allyl complexes are treated in Chapter 4. Based on the reactions of those pseudohalides, several benzene derivatives such as aniline, phenol, benzoic acid and benzenesulfonic acid can be used for the reaction, in addition to phenyl halides. In Scheme 3.1, reactions of benzene as a parent ring compound are summarized. Needless to say, the reactions can be extended to various aromatic compounds including heteroaromatic compounds whenever their halides and pseudohalides are available. 

The most characteristic catalytic activity of the rhodium complex was observed with the reaction of aroyl halides. The decarbonylation of aroyl halides was not satisfactory with palladium catalyst whereas they decarbonylated smoothly on heating to 200°C. with the rhodium complex. For example, when benzoyl chloride was heated with the complex at 200°C., chlorobenzene distilled oflF rapidly ith the evolution of carbon monoxide. Benzoyl bromide reacts similarly to give bromo-benzene. Phenylacetyl chloride was coi verted into benzyl chloride. Additional results are in Table II. 

The acid chlorides of several chromone-2-carboxylic acids have been used in the Freidel-Crafts reaction to prepare 2-aroyl-chromones which were pharmacologically active.Decarboxylation of a heterocyclic acid is often a facile reaction but removal of an aldehyde group is unusual. Chromone-3-carboxaldehyde (156) has been decarbonylated by heating with piperidine to give the acrylophenone (157), which cyclized again, with loss of piperidine and one carbon atom. ... 

The acylpalladium halide complex 84 is an intermediate of catalytic decarbony-lation of aroyl halides 83 [53]. The decarbonylation of 84 generates the aryl-palladium intermediate 85 at higher temperature which undergoes facile alkene insertion. Therefore, similar to aryl halides, acyl halides can be used for the alkene insertion. The reaction is carried out with a phosphine-free Pd catalyst in the presence of tertiary amines [54]. Higher yields were obtained by using a mixture of K2CO3 and benzyltrioctylammonium chloride [55]. 

Ghlorotris(triphenylphosphine) rhodium causes the decarbonylation of aroyl to aryl chlorides in excellent yields at relatively low temp. At higher temp., only catalytic amounts of the reagent are required. — E A mixture of henzoyl chloride, the above Rh-compound, and benzene heated 15 min. at 80° chlorobenzene. Y almost 100%. F. e. s. J. Blum, Tetrah. Let. 1966, 1605 chlorides from sulfonic acid chlorides s. Tetrah. Let. 1966, 3041 also ethylene derivatives from carboxylic acid chlorides s. J. Tsuji and K. Ohno, Am. Soc. 88, 3452 (1966) Tetrah. Let. 1966, 4713. 

---