Arylation of enones

Reductive arylation of enones, TiCl3 induces homolytic dediazotization of diazonium salts to produce aryl radicals, which arylate electron-deficient alkenes.1 Example ... 

Scheme 27).A 6-arylation of enones using thallium reagents 104... 

Racemic Rh-BINAP catalyst has been employed in the arylation of enones with ArInCl2, which proceeds in THF-MeOH at 110 Conjugate hydrosilylation of diarylacrylates Ar Ar C=CHC02R with (EtO)2MeSiH, catalysed by the Rh-Phebox complex (515), has been reported to proceed with <99%... 

Instead of employing arylboronic acids and related reagents for the Rh-catalysed fl-arylation of enones, the same goal can now be achieved through the C-H activation of the nucleophilic partner. Thus, arenes with a directing group, such as the a-pyridine substituent in (516), have been added to chalcone and related enones, giving rise to (517)... 

Regiocontrolled q- or / -alkenylation and arylation of cyclic enones are possible without protection of the ketone by applying the coupling reaction of the Q- or /3-halo enones 607 and 608 with aryl and alkenylzinc reagents[468,469]. 

Combination of nickel bromide (or nickel acetylacetonate) and A. A -dibutylnorephcdrinc catalyzed the enantioselective conjugate addition of dialkylzincs to a./Tunsaturated ketones to afford optically active //-substituted ketones in up to ca. 50% ee53. Use of the nickel(II) bipyridyl-chiral ligand complex in acetonitrile/toluenc as an in situ prepared catalyst system afforded the //-substituted ketones 2, from aryl-substituted enones 1, in up to 90% ee54. 

Certain catalysts promote the reduction of ketones with organosilanes. The reduction of acetophenone with Et3SiH is catalyzed by the diphosphine 65 and gives only a small amount of overreduction to ethylbenzene.377 Aryl alkyl enones and ynones are reduced to the corresponding alcohols with triethoxysilane and the titanium-based catalyst 66.378 Trichlorosilane reduces acetophenone in 90% yield with /V-formylpyrrolidinc catalysis.379... 

Aryl-substituted enones such as chalcone and benzalacetone have been used as model substrates in the study of asymmetric 1,4-addition of acyclic enones. Many chiral ligands have been found to afford good enantioselectivities (Scheme 19). Typical results are summarized in Table i 46>50 58-66... 

Aryl-substituted enones (chalcones in particular) have been used as model substrates in studies of catalytic 1,4-additions vith organozinc reagents. Fig. 7.7 summarizes typical enantioselectivities achieved vith various chiral ligands. 

Acyclic Enones as Substrates Compared to cyclic enones, acyclic enones are generally more challenging substrates for the copper-catalyzed asymmetric 1,4-addition reactions. Several ligands have been reported that can achieve high ee when p-aryl acyclic enones are used as substrates in the 1,4-addition of diethyl-zinc (Figure 3.5). ° ... 

Hayashi et al. and Miyaura et al. have reported that far less nucleophilic aryl- and alkenyl-boronic acids can react with a variety of enones in the presence of a BINAP-rhodium catalyst to give adducts with high enantiopurity in general (Scheme 8D.5) [13], The one pot procedure, involving the hydroboration of alkynes as the first step (R = alkenyl), was achieved in the presence of amines without affecting the enantioselectivity [13]. 

SCS-MP2 and the new perturbative B2-PLYP density functional methods provide accurate reaction barriers and outperform MP2 and B3-LYP methods when applied to the 1,3-dipolar cycloaddition reactions of ethylene and acetylene.39 Phosphepine has been shown to catalyse the asymmetric 3 + 2-cycloaddition of allenes with a variety of enones (e.g. chalcones) to produce highly functionalized cyclopentenes with good enantiomeric excess.40 The AuPPh3SbF6 complex catalysed the intramolecular 3 + 2- cycloaddition of unactivated arenyne- (or enyne)-yne functionalities under ambient conditions.41 A review of the use of Rh(I)-catalysed 3 + 2-cycloadditions of diaryl-and arylalkyl-cyclopropenones and aryl-, heteroaryl-, and dialkyl-substituted alkynes to synthesise cyclopentadienones for use in the synthesis of natural products, polymers, dendrimers, and antigen-presenting scaffolds has been presented.42... 

The Julia-Colonna method, which uses polyleucine, can form an epoxide from a chalcone (Scheme 9.17).126-132 However, the method is limited to aryl-substituted enones and closely related systems, and even then scale up of the procedure has been found to be problematic.133 The product of the epoxidation 14 has been used in a synthesis of (+)-clausenamide (15).134... 

In a related case, Maier and coworker [153] have recently also demonstrated that vinylogous enolates can enter into a cross-coupling step. However, the final products of Pd-catalyzed reactions of the hexahydro naph-thalenone and aryl bromides or iodides in the presence of cesium carbonate and tetraalkylammonium bromide in DMF at room temperature are 7-aryltetralones 208 (Scheme 85). This process can be readily interpreted as a Pd-catalyzed /-selective arylation of the thermodynamic enone enolate with a concomitant dehydrogenation-aromatization of the initial crosscoupling product. 

Benzotriazole was found to be an efficient ligand for the Cu(I) iodide-catalyzed N-arylation of imidazoles with aryl and heteroaryl halides <07TL4207>. The first enantioselective conjugate addition reaction of I //-benzotriazole with a variety of enones catalyzed by a cinchona alkaloid thiourea affords Michael adducts in good yields with moderate to good enantioselectivities has been reported <07S2576>. 

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