Electron-deficient aromatic

Electron-Deficient Polymers - Luminescent Transport Layers 16 Other Electron-Deficient PPV Derivatives 19 Electron-Deficient Aromatic Systems 19 Full Color Displays - The Search for Blue Emitters 21 Isolated Chromophores - Towards Blue Emission 21 Comb Polymers with Chromophores on the Side-Chain 22 Chiral PPV - Polarized Emission 23 Poly(thienylene vinylene)s —... 

With electron-deficient aromatic substrates (Entries 4 and 5), high yields and selectivities were observed, but enantioselectivities were variable and solvent-de-pendent (compare Entry 6 with 7 and see Section 1.2.1.3 for further discussion). With a,P-unsaturated tosylhydrazone salts, selectivities and yields were lower. The scope of this process has been extensively mapped out, enabling the optimum disconnection for epoxidation to be chosen [10]. 

The fourth factor becomes an issue when anti betaine formation is reversible or partially reversible. This can occur with more hindered or more stable ylides. In these cases the enantiodifferentiating step becomes either the bond rotation or the ring-closure step (Scheme 1.12), and as a result the observed enantioselectivities are generally lower (Entry 5, Table 1.5 the electron-deficient aromatic ylide gives lower enantioselectivity). However the use of protic solvents (Entry 6, Table 1.5) or lithium salts has been shown to reduce reversibility in betaine formation and can result in increased enantioselectivities in these cases [13]. Although protic solvents give low yields and so are not practically useful, lithium salts do not suffer this drawback. [18]... 

In another nonelectrolytic process, arylacetic acids are converted to vi c-diaryl compounds 2A1CR2COOH —> ArCR2CR2Ar by treatment with sodium persulfate (Na2S20g) and a catalytic amount of AgNOs." Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2 ArCOCl —> ArAr) by treatment with a disilane RsSiSiRs and a palladium catalyst." " ... 

This method is particularly useful for electron-deficient aromatic aldehydes, but it is not efficient with aliphatic aldehydes, probably a consequence of competitive aldol reaction. 

Bagley and coworkers have described the preparation of primary thioamides by treatment of nitriles with ammonium sulfide in methanol solution (Scheme 6.139) [276], While the reactions with electron-deficient aromatic nitriles proceeded at room temperature, other aromatic and aliphatic nitriles required microwave heating at 80-130 °C for 15-30 min to furnish the thioamides in moderate to high yields. This protocol avoids the use of hydrogen sulfide gas under high pressure, proceeds in the absence of base, and usually provides thioamides without the need for chromatographic purification. 

Nucleophilic attack by a trialkyl phosphite on a significantly electron-deficient aromatic ring involving addition-elimination of a nitro group (as nitrite anion), which completes the final step of the normal Michaelis-Arbuzov reaction (Figure... 

Quite recently, the same research group compared the electrophilicity of 6-nitro-tetrazolo[l,5- ]pyridine and 6,8-dini-trotetrazolo[l,5- ]pyridine 11 with a series of electron-deficient aromatic and heteroaromatic compounds <2005JOC6242>. As reference nucleophiles, fV-methylpyrrole, indole, fV-methylindole, and some morpholino enamines were used. The reactivity of the electrophiles studied followed the linear-free energy relationship defined by Mayr et al. <2003ACR66>. 

E. Buncel, in The Chemistry of Functional Groups, Supplement F (Ed. S. Patai), Chap. 27, Wiley, Chichester 1982 E. Buncel, M. R. Crampton, M. J. Strauss and F. Terrier, Electron-Deficient Aromatic- and Heteroaromatic-Base Interactions, Elsevier, Amsterdam, 1984. 

Electron Deficient Aromatic- and Heteroaromatic-Base Interactions. 

The Baylis-Hillman reaction (Scheme 3) of ethyl vinyl ketone with electron-deficient aromatic aldehydes (e.g. where R = 0-NO2C6H4), in MeCN or EtCN solution, has been found to proceed enantioselectively in presence of catalytic base (32) derived from proline. The Michael adduct formed between the catalyst and the vinyl... 

Nucleophilic substitutions of simple aromatic compounds which formally involve a hydride displacement are difficult to achieve because of the poor leaving group and the high electron density of the aromatic nucleus which repels approach of a nucleophile. However, rc-electron deficient aromatic compounds such as metal carbonyl complexes are susceptible to attack by certain carbon nucleophiles. Studies of this chemistry have shown [16] an opposite jegioselectivity to the corresponding electrophilic substitutions, in agreement with the polarity alternation rule. 

For a monograph on Meisenheimer salts and on this mechanism, see Buncel Crampton Strauss Terrier Electron Deficient Aromatic- and Heteroaromatic-Base Interactions Elsevier New York. 1984. For reviews of structural and other studies, sec Illuminati Stcgcl Adv. Heterocvcl. Chem. 1983,34. 305-444 Artamkina Egorov Bcletskava Chem. Rev. 1982.82. 427-459 Terrier Chem. Rev. 1982, 82. 77-152 Strauss Chem. Rev. 1970, 70. 667-712. Ace. Chem. Res. 1974, 7. 181-188 Hall Poranski. in Fcucr The Chemistry of the Nitro and Niiroso Groups, pt, 2. Wiley New York. 1970. pp. 329-384 Crampton, Adv. Phvs. Org. Chem. i969, 7, 211-257 Foster Fyfe Rev. Pure Appl. Chem. 1966. 16, 61-82. 

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