Aryl groups variation

With alkyl aryl ketones, it is the aryl group that generally migrates to the nitrogen, except when the alkyl group is bulky. The reaction has been applied to a few aldehydes, but rarely. With aldehydes the product is usually the nitrile (16-21). Even with ketones, conversion to the nitrile is often a side reaction, especially with the type of ketone that gives 17-31. A useful variation of the Schmidt reaction treats a cyclic ketone with an alkyl azide (RN3) in the presence of TiCU, generating a... 

Ru—C(carbene) bond distances are shorter than Ru—P bond lengths, but this can simply be explained by the difference in covalent radii between P and The variation of Ru—C(carbene) bond distances among ruthenium carbene complexes illustrates that nucleophilic carbene ligands are better donors when alkyl, instead of aryl, groups are present, with the exception of 6. This anomaly can be explained on the basis of large steric demands of the adamantyl groups on the imidazole framework which hinder the carbene lone pair overlap with metal orbitals. Comparison of the Ru—C(carbene) bond distances among the aryl-substituted carbenes show... 

Another important variation of the Staudinger ligation reaction described above involves the use of cleavable aryl groups on the triphenylphosphine component, which allows for... 

Modified CNTs feature various spectral changes depending on the methods and the location of modifications. These changes include variations in band frequencies, width, and intensities. For example, aryldiazonium salts [139] were used to modify individual sodium dodecyl sulphate (SDS) coated SWNTs with aryl group. The Raman spectrum of functionalized (SDS-free) SWNTs shows a disorder mode much higher than pristine SWNT the radial breathing modes are nearly unobservable. 

More recently a variation of this mechanism was reported by Novak [37], The mechanism involves nucleophilic attack at co-ordinated phosphines and it explains the exchange of aryl groups at the phosphine centres with the intermediacy of metal aryl moieties. After the nucleophilic attack the phosphine may dissociate from the metal as a phosphonium salt. To obtain a catalytic cycle the phosphonium salt adds oxidatively to the zerovalent palladium complex (Figure 2.38). Note where the electrons go . 

The use of cyclic alkenes as substrates or the preparation of cyclic structures in the Heck reaction allows an asymmetric variation of the Heck reaction. An example of an intermolecular process is the addition of arenes to 1,2-dihydro furan using BINAP as the ligand, reported by Hayashi [23], Since the addition of palladium-aryl occurs in a syn fashion to a cyclic compound, the 13-hydride elimination cannot take place at the carbon that carries the phenyl group just added (carbon 1), and therefore it takes place at the carbon atom at the other side of palladium (carbon 3). The normal Heck products would not be chiral because an alkene is formed at the position where the aryl group is added. A side-reaction that occurs is the isomerisation of the alkene. Figure 13.20 illustrates this, omitting catalyst details and isomerisation products. 

The radical-cation is relatively stable when the 1-aryl group has a para-substituent and can be characterised by uv-spectroscopy [34], When this para-substituent is not present, two radical-cations dimerise by carbon-carbon bond formation at this position, followed by loss of two protons. The rate constant for this dimerization step can be deduced from the variation of the rotating disc elec-... 

Situations arise when it is necessary to consider the parent as a one-carbon chain. In such circumstances, RC02H becomes a substituted carboxylic acid. This variation is met most frequently when R is a cycloalkyl or aryl group ... 

In a related study, the Shibasaki group examined cyclizadon of naphthyl triflate 10.1 (Scheme 8G.10) [23], Cyclization of 10.1 under standard cationic conditions gave Heck product 10.2 in 78% yield and 87% ee. Evidently, the reaction is fairly tolerant of the nature of the aryl group, because both 10.1 and 9.3 behaved similarly. An interesting variation of this reaction was also demonstrated in which Suzuki coupling and asymmetric Heck cyclization were performed in a one-pot operation. Thus, treatment of ditriflate 10.3 with borane 10.4 under standard Heck conditions provided 10.2 in similar enantioselectivity to the stepwise procedure, albeit in quite low yield. Heck product 10.2 was converted in several steps to the natural products, halenaqui-none (10.5) and halenaquinol (10.6). 

The availability of a wide range of P(III) compounds from the work with activated alkenes,which is relevant to the dimeri-sation of acrylonitrile, facilitated the determination of p-values (Table II) for a number of substrates by systematic variation of the para-substituents in the aryl groups on phosphorus. The data... 

Class b) represents a set of phosphane oxides, phosphane sulfides and phosphane selenides (X = PR3) where R is an alkyl or aryl group. The principal values of the 31P chemical shift tensors are shown in Table 2. The chemical shift anisotropy values Ao are large and comparable to the 31P chemical shift anisotropy variation observed in the liquid phase by change of coordination or of functionality around the phosphorus. It is noteworthy that in P(CH3)3 and PCC6H5)3 the chemical shift anisotropies are much smaller, 8 ppm and 24 ppm respectively. For a given R group, the chemical shift anisotropies range in the order Ao(0-PR3) >... 

Yet another variation on the same theme links the two aryl groups together 32 34 to form spirofluorenylidene (18) spirosuberenylidene (19) and the like (Figure 3.7). The photochromic properties of these compounds (intense and slow to fade) are best explained if one considers them di-ortho-substituted 3,3-diaryl-3//-naphtho[2,l-... 

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