Carbonylation reactions, of organic halides

Synthetic applications of palladium-catalyzed carbonylation reactions of organic halides and pseudohalides have recently been reviewed [6]. We here focus only on selected applications with particular emphasis on the pioneering as well as some of the most recent examples of palladium-catalyzed carbonylation reactions of enol triflates and iodoalkenes. 

In 1979 the reaction of benzyl and aryl halides was reported with mechanistic discussions [8, 9]. The first palladium-catalyzed carbonylative coupling of organic halides with organotin compounds was reported by Tanaka in the same year (Scheme 4) [10,11]. 

Cobalt catalysts were used for substitution reactions of organic halides [442] and a small-ring enol lactone [Eq. (201) 443]. The cobalt salt seems to be the most effective one among a few transition metal salts involving copper, nickel, [see Eq. (130)], and iron. Without the catalyst, Grignard reagent attacked the carbonyl carbon of the enol lactone to give a mixture of a few ketonic compounds in a low yield. 

Utimoto, K., Matsubara, S. Samarium diiodide-mediated reaction of organic halides with carbonyl compounds. Yuki Gosei Kagaku KyokaishitOOS, 56, 908-918. 

As mentioned in Sect. 2.3, Inanaga and co-workers have demonstrated that Barbier-type reactions of organic halides with carbonyl compounds are promoted by addition of HMPA [16]. They reported a mild convenient method for the direct synthesis of lactones from bromo esters and ketones or aldehydes by using a HMPA-promoted Barbier-type reaction with Sml2 (Scheme 13). They also found that the SmI2/THF-HMPA system was highly useful for the generation of... 

In this section we describe ketone synthesis via Pd-catalyzed carbonylative crosscoupling reaction of organic halides (and triflates, RX) and organometallic reagents (R M, Scheme 1). 

The Pd-catalyzed carbonylative cross-coupling reaction of organic halides (or triflates) with organostannanes is an especially valuable and versatile synthetic method of un-symmetrical ketone. One serious drawback is the high toxicity of organostannanes. 

G. Reactions of Organic Halides and Transition Metal Carbonyl... 

In both this and the previous method of preparation, low yields are often found, due to competitive coupling reactions or to further reactions such as the decomposition of the M— R], products. Also tire metal anions are strong nucleophiles and they may cause the or mic halides to undergo elimination reactions. Metal-acyl complexes are often by-products of the reaction of organic halides with the metal carbonyl anions they are formed by insertion reactions (see p. 258). Indeed, acyl halides may be used to give metal-acyl complexes which are dien decarbonylated either thermally or by photochemi techniques [. Some metal-aryl complexes which are... 

Carbonylation is an exceedingly broad subject, but the main reaction patterns can be easily rationalized by recalling the classification used earlier for coupling reactions involving (a) metallacycles (b) hydride-promoted reactions and (c) oxidative addition of organic halides to zero-valent nickel. In fact, one or other of these steps is necessary to form a species able to undergo carbonylation. 

Silver(I)-ion- assisted Me2SO oxidations of organic halides have been observed for primary and secondary bromides and iodides (174). The reactions occur under ambient conditions yielding the corresponding carbonyl, plus traces of alcohol. The fate of the silver ion is unreported. 

Carbon monoxide and low valent transition metals are known to give various quite well described complexes. However, due to the strong coordination to CO, these metal carbonyl compounds are not very reactive towards carbon-halogen bonds. Thus the carbonylation of organic halides remains a difficult reaction since the presence of CO leads to the deactivation of the catalytic system. Various attempts to overcome this drawback have however been reported. 

It has been shown very recently that carbonylation reactions can also be performed by electrolyzing under CO a solution of organic halide containing... 

The mechanism of palladium-catalyzed carbonylation of organic halides is generally assumed to involve oxidative additon of R-X to a Pd(0) species which is formed from the precursors on the action of CO + OH . Migratory insertion of R onto a coordinated CO followed by reaction with a nucleophile generates the product and gives back the catalytically active palladium(O) species (Scheme 5.4 A). 

With a combination of organic halide, alkene or alkyne, and palladium catalyst, the reaction may take a superficially similar, but different pathway other than a Heck-type reaction. In these, the halogen is retained in the products, as an alkyl or vinyl halide. These results occur when the starting organic halide is allyl, a- to a carbonyl or similar group, or attached to a perhalogenated carbon atom. In much of the early work, mixtures with Hecklike elimination products were obtained, due to elimination caused by the presence of amine bases in the reaction mixture (equation 165)323. 

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