Esters from aryl halides

The direct preparation of arylboronic esters from aryl halides or triflates now allows a one-pot, two-step procedure for the synthesis of unsymmetrical biaryls (Scheme 1-41) [147]. The synthesis of biaryls is readily carried out in the same flask when the first coupling of the triflate with diboron 82 is followed by the next reaction with another triflate. The synthesis of naturally occurring biflavanoids and the couphng of N-(phenylfluorenyl)amino carbonyl compounds to polymeric supports are reported [154]. 

Scheme 2.32 Palladium-catalysed synthesis of esters from aryl halides with Mo(CO)6 as the carbon monoxide source (DMAP = 4-dimethylaminopyridine).

Ready availability of arylboronic esters from aryl halides or triflates (Eqs. 13 and 14) now offers a one-pot, two-step procedure for synthesizing unsymmetrical biaryls. The cross-coupling reaction of bis(pinaco-lato)diboron with triflate in dioxane is followed by a subsequent coupling with another triflate in the presence of K3PO4 to furnish an unsymmetrical biaryl from two triflates (Eq. 63). The synthesis from two different... 

Rapid palladium-catalyzed synthesis of esters from aryl halides utilizing Mo (CO)4 as a sohd carbon monoxide somce. Journal of Combinatorial Chemistry, 5, 350-352. 

The palladium-catalyzed Heck carbonylation reaction is a powerful means of generating amides, esters, and carboxylic acids from aryl halides or pseudohalides [28]. The development of rapid, reliable, and convenient procedures for the introduction of carbonyl groups is important for the development of high throughput chemistry in general and high-speed microwave-mediated chemistry in particular. Unfortunately, the traditional method of introducing carbon monoxide into a reaction mixture via a balloon or gas tube is not practical because of the special requirements of microwave synthesis. 

Some noncyclic thioacetals are sometimes used for the preparation of keto acids from aryl halides or keto esters by 1,4-addition on a,p-unsaturated ketones (Scheme 3). 

Very recently, arylboronic esters have been directly obtained from aryl halides via the cross-coupling reaction of (tetraalkoxy)diboron (Scheme 2-7) [28]. The reaction tolerates various functional groups such as ester, nitrile, nitro, and acyl groups. 

In addition, reductive elimination of palladium and nickel complexes to form esters (Equations 8.67 and 8.68), amides, and tiiioesters has been reported. -" The reductive eliminations of esters and amides were observed during mechanistic studies on the palladium-catalyzed formation of esters and amides from aryl halides, carbon monoxide, and alcohols or amines. This catalytic process is presented in Qiapter 17 (carbonylation processes). The reductive elimination of thioesters from nickel complexes were studied, in part, to understand the C-S bond-forming process of acetyl coenzyme A synthase. Prior to this work, an iron-mediated synthesis of p-lactams had been reported that appears to occur by reductive elimination to form the amide C-N bond of the lactam. ... 

A method for synthesizing esters from aryl, vinyl, and benzyl halides and alcohols under carbon monoxide in the presence of a palladium catalyst was developed in 1974. " In a similar manner, syntheses of amides or carboxylic acids were also subsequently achieved using primary or secondary amines or water instead of alcohols (Scheme 1). 

Several papers deal with the products of (formally) "double carbonylation" reactions. The carbonylation product of styrene oxide in the presence of a Co2(C0)g/MeI catalyst under phase-transfer conditions contains two CO derived carbons (eqn.17). Two groups report the synthesis of a-keto esters from aryl iodides, CO, alcohols and tertiary amines the selectivity depends on Replacement of alcohol by water leads to a-keto acids. a-Keto-amides are prepared similarly from secondary amines. In this case the mechanism has been studied in detail oxidative addition of the aryl halide is the rate-determining step (Scheme 5). °... 

The o-keto ester 513 is formed from a bulky secondary alcohol using tricy-clohexylphosphine or triarylphosphine, but the selectivity is low[367-369]. Alkenyl bromides are less reactive than aryl halides for double carbonyla-tion[367], a-Keto amides are obtained from aryl and alkenyl bromides, but a-keto esters are not obtained by their carbonylation in alcohol[370]. A mechanism for the double carbonylation was proposed[371,372],... 

Since the exocyclic sulfur is more reactive in the ambident anion than in A-4-thiazoIine-2-thione. greater nucleophilic reactivity is to be expected. Thus a large variety of thioethers were prepared in good yields starting from alkylhalides (e.g.. Scheme 38 (54, 91, 111, 166-179). lactones (54, 160), aryl halides (54, 152. 180, 181), acyl chlorides (54. 149, 182-184). halothiazoles (54, 185-190), a-haloesters (149. 152. 177. 191-194), cyanuric chloride (151). fV.N-dimethylthiocarbamoyl chloride (151, 152. 195. 196), /3-chloroethyl ester of acrylic acid (197), (3-dimethylaminoethyl chloride (152). l,4-dichloro-2-butyne (152), 1,4-dichloro-2-butene (152), and 2-chloro-propionitrile (152). A general... 

For the synthesis of a suitable arylboron compound, usually an aryl halide is converted to an aryllithium or aryl Grignard derivative, and then reacted with a trialkoxyborane to yield an arylboronic ester, e.g. the phenylboronic acid diisopropyl ester 13 from bromobenzene 11 ... 

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