Arylation aryl

The Aggarwal group has used chiral sulfide 7, derived from camphorsulfonyl chloride, in asymmetric epoxidation [4]. Firstly, they prefonned the salt 8 from either the bromide or the alcohol, and then formed the ylide in the presence of a range of carbonyl compounds. This process proved effective for the synthesis of aryl-aryl, aryl-heteroaryl, aryl-alkyl, and aryl-vinyl epoxides (Table 1.2, Entries 1-5). 

A. Aryl-Aryl, Aryl-Alkenyl and Alkenyl-Aryl Coupling Reactions. 483... 

Three transmetallation reactions are known. The reaction starts by the oxidative addition of halides to transition metal complexes to form 206. (In this scheme, all ligands are omitted.) (i) The C—C bonds 208 are formed by transmetallation of 206 with 207 and reductive elimination. Mainly Pd and Ni complexes are used as efficient catalysts. Aryl aryl, aryl alkenyl, alkenyl-alkenyl bonds, and some alkenyl alkyl and aryl-alkyl bonds, are formed by the cross-coupling, (ii) Metal hydrides 209 are another partner of the transmetallation, and hydrogenolysis of halides occurs to give 210. This reaction is discussed in Section 3.8. (iii) C—M bonds 212 are formed by the reaction of dimetallic compounds 211 with 206. These reactions are summarized in Schemes 3.3-3.6. 

The aryl-aryl, aryl-heteroaryl, and heteroaryl-heteroaiyl couplings have also been extensively applied in synthesis. Only a few examples of the most recent results within the context of complex natural product synthesis will be summarized here. 

GOMBERG - BACHMANN - GRAEBE ULLMANN Arylation Aryl-aryl bond formation via diazomum salts Carbazola synthesis by intramolecular aryl-aryl bond formation. 

Stille coupling. The many examples describing applications of this C-C bondforming method attest to its versatility. A comprehensive study of the coupling of arylstannanes with sulfonates has appeared. Of course, various combinations of aryl/aryl, aryl/vinyl, and vinyl/vinyl couplings are equally possible. PhsAs is often added to the reaction media, and in other cases Cul acts as a cocatalyst. 

Notable variations may occur, particularly in the proportions of heteroatoms such as oxygen and sulfur, but they are always exposed in a very characteristic manner. For example, nitrogen occurs in the asphaltenes in various heterocyclic chains, the oxygen can be identified as carboxylic, phenolic and ketone (Speight et al, 1994) while sulfur is in the form of thiols, thiophenes, benzothiophenes, dibenzothiophenes and naphtebenzothiophenes as well as in systems such as sulphide, alkyl-aryl, aryl-aryl and alky- laryl (Speight et al, 1984). 

The observation that acylsilanes such as 17 could directly provide intermediate 18 via cyanide addition and [l,2]-Brook rearrangement has led to an improved process that is catalytic in cyanide. The reaction produces O-silylated aryl-aryl, aryl-alkyl, and alkyl-aryl acyloin products in moderate to high yield.Further work by Johnson and co-workers established the superiority of lanthanum tricyanide for this process, which allows selective access to even alkyl-alkyl acyloin products. ... 

It was also demonstrated that a-heteroatom-substituted alkyltributyltins cross-coupled in the presence of catalytic amounts of Cu [157]. This catalytic use of copper salts was extended to various aryl-aryl, aryl-heteroaryl and aryl-vinyl crosscouplings [158]. 

The oxidative coupling of toluene using Pd(OAc)2 via />-tolylmercury(II) acetate (428) forms bitolyl[384]. The aryl-aryl coupling proceeds with copper and a catalytic amount of PdCl2 in pyridine[385]. Conjugated dienes are obtained by the coupling of alkenylmercury(II) chlorides[386]. 

Other pseudo-halides are used for carbonylation. Phenyl tluorosulfonate (484) can be carbonylated to give benzoate[337]. Aryl(aryl)iodonium salts[338], aryl(alkenyl)iodonium salts (485)[339], and arylialkynyl)iodonium salts (486)[340] are reactive compounds and undergo carbonylation under mild conditions (room temperature, 1 atm) to give aryl, alkenyl, and alkynyl esters. lodoxybenzene (487) is carbonylated under mild conditions in... 

These aryl—aryl couplings are appHcations of the Ni(0) and Ni(II)-cataly2ed cross-couplings of unreactive organic haUdes with Grignard reagents. This work has been extensively reviewed (90). 

In addition to sodium, other metals have found application for the Wurtz coupling reaction, e.g. zinc, iron, copper, lithium, magnesium. The use of ultrasound can have positive effect on reactivity as well as rate and yield of this two-phase reaction aryl halides can then even undergo an aryl-aryl coupling reaction to yield biaryls. ... 

One of the first examples was the above mentioned work from Yoshino et al. [7] concerning the synthesis of poly(9,9-dialkylfluorene)s via oxidative coupling of fluorene derivatives. Poly(9,9-dialkylfluorene) derivatives have been also synthesized via Ni- and Pd-catalyzed aryl-aryl homo- and cross-coupling reactions of sui-... 

The authors used a synthesis of 9,9-spirobitluorenes 32 which was developed by Clarksen and Gomberg [60] and which includes the addition of biphenyl-2-yl-magnesium iodide to fluorenone and subsequent cyclization with protic acids. To obtain 2,2,, 7,7 -arylated 9,9-spirobifluorenes 33, 9,9-spirobifluorene (32) was tetrabrominated [58] to yield 34 followed by a Suzuki-type aryl-aryl cross-coupling with various oligoaryl and oligoheteroaryl boronic acids to obtain the 2,2, 7,7 -tetraarylated derivatives 33. 

In a classical multi-step route the critical point is to conduct (he ring closure quantitatively and regioseleclively. In the synthesis of I.PPP, the precursor polymer 13 is initially prepared in an aryl-aryl coupling from an aromatic diboronic acid and an aromatic dibromoketone. 

In addition, Suehiro et al. (1987) were able to accurately determine the rates of dediazoniation of twenty substituted aryldiazenyl radicals formed from aryl(aryl-thio)diazenes (Scheme 8-36), in cyclopropane and in alkenic solvents at -48 to — 117°C, using a time-resolved ESR method. 

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