Halides, aryl, arylation carbonylation

Palladium complexes also catalyze the carbonylation of halides. Aryl (see 13-13), vinylic, benzylic, and allylic halides (especially iodides) can be converted to carboxylic esters with CO, an alcohol or alkoxide, and a palladium complex. Similar reactivity was reported with vinyl triflates. Use of an amine instead of the alcohol or alkoxide leads to an amide. Reaction with an amine, AJBN, CO, and a tetraalkyltin catalyst also leads to an amide. Similar reaction with an alcohol, under Xe irradiation, leads to the ester. Benzylic and allylic halides were converted to carboxylic acids electrocatalytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions. ... 

The hydrazone group is hydrolyzed (16-2) during the course of the reaction. Yields are high. Aryl iodides are converted to unsymmetrical diaryl ketones on treatment with aryImercury halides and nickel carbonyl ArH-Ar HgX-l-Ni(CO)4 ArCOAr... 

DECOMPOSITION OF INORGANIC OXIDES AND SULPHIDES HALIDES AND DERIVATIVES METAL ALKYLS, ARYLS, CARBONYLS AND NITROSYLS... 

Electrophilic ring closure of aryl-substituted compounds such as alkenes, halides, alcohols, and carbonyl compounds called cyclialkylation can be induced by conventional Friedel-Crafts catalysts309 and by superacids. Examples are also known in which an intermolecular alkylation step is followed by intramolecular alkylation of the intermediate to furnish a cyclic product. 

C-H bonds in hydrogenation reactions, 276-277 C-Si bonds, 73 Carbonyl complexes, 184 Carbonyl hafnium complex, 144 Carbonylation of aryl halides, 271-272 Carbonylation reactions in ionic liquids, 271... 

Several electrochemically mediated Ni-catalyzed addition reactions with aryl halides were reported, but their mechanism is not fully clarified. Using 10 mol% of NiBr2 as a catalyst, heteroaryl halides were added to a, p-unsaturated carbonyl compounds affording (1-aryl carbonyl compounds in 15-86% yield [127]. These addition reactions seem to proceed rather by classical Ni(0)-Ni(II) or Ni(I)-Ni(III) catalytic cycles than by a radical catalysis mechanism. 

Aryl halides may be carbonylated using several different palladium complexes and several different hydrogen donors839,840,842,843. In most synthetically useful reactions the conditions are reasonably low pressure (up to 6 bar) and reasonably low temperatures (below 100 °C). Halobenzenes have also been successfully carbonylated at 30 bar using a carbon monoxide/hydrogen mixture in the presence of a palladium catalyst and triethy-lamine. In this case the halobenzene must first be complexed with chromium tricarbonyl844. 

The cross-coupling of aryl halides and enolates is a powerful method to prepare a-arylated carbonyl compounds that are difficult to access through classic organic chemistry [29]. (NHC)Pd(allyl)Cl species [30] were the first NHC-bearing complexes used as pre-catalysts for the a-arylation of ketones [31,32]. More recently, novel (IPr)Pd(acac)Cl complexes have shown remarkable catalytic activity in this transformation [33]. From aryl chlorides, excellent yields were obtained after short reaction times at 60 °C, the lowest temperature reported to date with a carbene-based system (Table 1). 

Keywords. Aryl halides, Arylation, Palladium catalysts. Carbonyl compounds. Aromatic compounds... 

Another method for the conversion of alkyl hahdes to carboxylic esters is treatment of a halide with nickel carbonyl Ni(CO)4 in the presence of an alcohol and its conjugate base. When R is primary, RX may only be a vinylic or an aryl halide retention of configuration is observed at a vinylic R. Consequently, a carbocation intermediate is not involved here. When R is tertiary, R may be primary alkyl as well as vinylic or aryl. This is thus one of the few methods for preparing esters of tertiary alcohols. Alkyl iodides give the best results, then bromides. In the presence of an amine, an amide can be isolated directly, at least in some instances. 

In contrast, nucleophilic attack at an sp -carbon center with anionic 18-electron species like [Co(CO)4] and [Fe(CO)4] usually fails to activate aromatic or vinylic halides. Thus, catalytic carbonylations of aryl halides are initiated by oxidative addition of a C-X bond to an electronically unsaturated metal complex, normally a palladium [7], cobalt [8] or nickel complex [9]. The rate of this oxidative addition decreases along the sequence... 

Aryl, vinyl, and benzyl halides are catalytically carbonylated by CO generated in situ from chloroform and aqueous alkali, in the presence of phosphine-palladium complexes such as PdCl2(PPh3)3. The biphasic reactions do not require a PT agent, they occur at r.t., and they afford the corresponding carboxylic acids in up to 92% yield. Labeling experiments with CHCb showed that the source of the Cl unit in the carbonylation is chloroform... 

Using poly(methylhydrosiloxane) (PMHS) as the hydrogen donor, aryl and benzyl halides can be carbonylated to aldehydes in the presence of [Pd(PPh3>4] under mild conditions (3 bar, 80 °C). The reaction only works for iodides 4-bromophenyl iodide, for example, is converted to 4-bromobenzaldehyde in 95% yield (equation 6). 

When a tertiary alcohol is formed by a Grignard reaction, the derived olefin is often easily obtained by warming the Grignard addition compound without isolation of the alcohol after treatment of the alkyl- or aryl-magnesium halide with the carbonyl compound and removal of the solvent, the residue is heated for a short time, whereupon the olefin distils off.12 In this way, for instance,... 

F.i. Reactions of Aryl and Vinyl Halides with Metal Carbonylates... 

While this cyclization method does not allow the incorporation of substituents into the 3-position, as is available with internal alkynes, in analogous chemistry to that in Section 6.2.2, the palladium bound intermediate of cyclization can be intercepted with a range of external reagents to functionalize this site. These include aryl or vinyl halides, allylic substrates, carbonylation, and Heck coupling with alkenes [72]. 

The discovery and development of the chemistry of Grignard reactions were especially important for applications to the synthesis of complex molecules because a new carbon-carbon bond is formed by combining two simpler building blocks, namely an alkyl or aryl halide and a carbonyl compound. The products of Grignard reactions also contain functionality that may then be used in subsequent transformations to fashion even larger molecules. 

Aryl halides can be carbonylated to give the corresponding carboxylic acids (Scheme 138) under very mild conditions in presence of inorganic bases (like alkaline metal hydroxides, carbonates, acetates etc.) and certain palladium catalysts (like Pd(OAc)2, K PdCl, Pd(NH3) Cl, PdCl2(PPh3)2 etc.). Best results are obtained with simple palladium salt using K2CO3 as base (Scheme 138). 

---