Monoaryls

In the reaction of the 1,1-dichloro-l-alkene 611 with phenylzinc chloride, only monoarylation takes place regioselectively to give the (Z)-l-chloro-l-phe-nylalkene 612[468,474],... 

Organophosphorus compounds. Phosphorus-carbon bond fonnation takes place by the reaction of various phosphorus compounds containing a P—H bond with halides or tritlates. Alkylaryl- or alkenylalkylphosphinates are prepared from alkylphosphinate[638]. The optically active isopropyl alkenyl-methylphosphinate 778 is prepared from isopropyl methylphosphinate with retention[639]. The monoaryl and symmetrical and asymmetric diarylphosphi-nates 780, 781, and 782 are prepared by the reaction of the unstable methyl phosphinate 779 with different amounts of aryl iodides. Tnmethyl orthoformate is added to stabilize the methyl phosphinate[640]. 

In all the diazotization reactions discussed in Sections 2.1-2.4 an equimolar amount of water is formed as byproduct. There are two general pathways for obtaining diazonium salts without formation of water. One is based on the rearrangement of 7V-nitroso-7V-arylacetamides, the other on the nitrosation of a monoarylated sp2-hybridized nitrogen compound by nitrosating reagents XNO in which X is a weak nucleophile. 

The use of excess diazoalkane in its reaction with sulfur dioxide will necessarily lead to symmetrically substituted thiirane dioxides. When monoalkyl or monoaryl diazoalkanes are used, mixtures of cis- and trans-isomers are formed18-19-99. 

An interesting observation in the solvolysis of all arylvinyl systems is the effect of added /3-aryl groups. All triarylvinyl substrates react more slowly than do the corresponding monoaryl or diaryl systems. For example, triphenylvinyl fluorosulfonate, 153, Ri =C6Hs, R = F, reacts about 2.5 times more slowly (140) in acetic acid than does a-phenylstyryl fluorosulfonate, 153, Rj = H, R = F. Similarly, trianisylvinyl bromide reacts 2.8 times and 1.2 times more slowly in 80% EtOH and in AcOH, respectively (144), than does cis-1,2-dianisylvinyl bromide. This difference probably results from increased hindrance to solvation and increased unfavorable steric interactions. 

Like similarly activated carboxylate esters, these aromatic phosphonate diesters 30 were readily hydrolyzed to GLYH3 in good yield and purity under typical strongly acidic or basic conditions, or in a stepwise fashion under extremely mild conditions via the zwitterionic monoaryl esters 32 (44). Products such as 32 or 33 readily precipitated after a few hours at room temperature from aqueous acetone. 

Monoalkylthallium(III) compounds are unstable (73, 79), and very few examples of this class have been isolated. A number of alkylthallium diacetates have been obtained either from oxythallation of olefins with thallium-(III) acetate (see below) or from exchange reactions such as that shown in Eq. (11) (74, 75). Only four alkylthallium dihalides have been isolated so far, namely a neopentylthallium dihalide (60) [Eq. (12)] and the isomeric 2-, 3-, and 4-pyridiomethylthallium dichlorides (20) [Eq. (13)]. Monoaryl-and monovinylthallium(III) derivatives are considerably more stable than... 

Finally, NHC complexes of copper, formed in situ from the hnidazolium salt and CuBr have been used in the monoarylation of aniline [167]. Trinuclear Cu(I) catalysts have been applied to the arylation of pyrazoles, triazoles, amides and phenols [168] (Scheme 6.50). 

A situation similar to that in acetyl phosphate is also encountered in benzoyl phosphate76 . Electron-attracting substituents on the phenyl ring accelerate the hydrolysis of the dianion (a linear relationship exists between log khydrol and the Hammett a constants with q = 1.2 and the linear log ki,j,drol./pKa relationship is the same as for the phosphoric monoaryl ester dianions65 . On the other hand, hydrolysis of the monoanion is influenced only slightly by substituents in the phenyl ring. These observations can also be rationalized in terms of the decomposition mechanism to the POf ion formulated for 116 and 117. 

Figure 2 Conversion of guaiacol (X), selectivity to vanillols (o), to monoaryl by-products (v) and to diaryl by-products (ct) as functions of the Si/AI ratio of H-mordenites. Reaction time, 2 h other reaction conditions as in Figure 1. H-mordenites were supplied by Engelhard.

CH-acids such as cyclopentadiene and indene give no monoarylation products under the conditions of cross-coupling, but rather are transformed into the exhaustively polyarylated... 

This procedure is the method of choice for the preparative chemist, since it not only provides the advantage of generally good yields (40—60%), but also can be carried out on a large scale. The modified Favorski reaction of dibromoketones offers a remarkably wide scope of application and has made possible the preparation of a large number of dialkyl-, diaryl-, and monoaryl cyclopropenones (see Table 1). Interestingly, the bicyclic cyclopropenones 5943) and 4041 have become accessible by use of the dibromoketone method. 

In a recent article by Botella and Najera, controlled mono- and double-Heck arylations in water catalyzed by an oxime-derived palladacycle were described [22], When the reaction was carried out under microwave irradiation at 120 °C in the presence of dicyclohexylmethylamine with only 0.01 mol% of palladium catalyst (palladium acetate or palladacycle), monoarylation took place in only 10 min with a very high turnover frequency (TOF) of > 40000 (Scheme 6.3). As regards diarylation, 1 mol% of the palladacycle catalyst and 2 equivalents of iodobenzene had to be utilized to obtain moderate to good yields of diarylated product. Whereas microwave heating at 120 °C provided a 31% yield after 10 min, a 66% isolated yield of product was obtained by heating the reaction mixture under reflux for 13 h at 100 °C. Here, the... 

It is noteworthy that quick and effective formation of diaryl nitrones can be achieved through oxidation of diaryl imines with Oxone (potassium peroxy-monosulfate) in such media as aqueous solution of NaHCC>3 in acetonitrile or acetone. When oxidized under such conditions, dialkyl or monoaryl imines give oxaziridines (17). Oxidation of 3,4-dihydroisoquinoline (9) with Oxone initially leads to the formation of oxaziridine (10) which is easily transformed into the corresponding 3,4-dihydroisoquinoline A-oxide (11) upon treatment with catalytic amounts of p-toluenesulfonic acid (Scheme 2.4) (18). 

Monoarylation of l-amino-4-hydroxyanthraquinone (6.39 X = OH) results in violet dyes such as Cl Disperse Violet 27 (6.44 R = H) and the bluish violet Cl Disperse Blue 72 (6.44 R = CH3) the latter dye is also important as Cl Solvent Violet 13. Chlorination of 1,4-diaminoanthraquinone with sulphuryl chloride gives the 2,3-dichloro derivative (Cl Disperse Violet 28), which on condensation with phenol yields Cl Disperse Violet 26 (6.45). Monoaryl or dialkyl derivatives of 1,4-diaminoanthraquinone (6.19 Cl Disperse Violet 1) are blue. Typical examples include Cl Disperse Blue 19 (6.46) and Cl Disperse Blue 23 (6.47). 

The arylation of phenols also proceeds smoothly. Even the sterically overcrowded 3,5-di- r/-butylphcnol 17 reacts with 2,4,6-trimethoxyphenyllead triacetate 18 to furnish compound 19, which is isolated in 87% yield, together with 10% of the monoarylation product (Equation (6)). 

The monoaryl Cl2BiC6H2-2,4,6-Ph3 is dimeric in the solid state with Bi-Cl distances of 3.074(1) A (bridging) and 2.532(1) A (terminal).135 The Bi-C bond length (2.266(4) A) is somewhat shorter than that found in the bis and tris aryls, probably as a result of the reduced steric crowding. The intermolecular Bi-Bi distance, 4.316(1) A, is shorter than the sum of the van der Waals radii, 4.68 A. Also, this molecule displays a Menshutkin interaction138 in which there is relatively close contact between bismuth and one of the pendant aryl groups resulting in a Bi-centroid distance of 3.53 A (calculated 4.04 A). 

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