A-Phenyl substitution

More recently, test products were created of a blend of PMMA with a phenyl-substituted methacrylate these products have a glass-transition temperature of around 125°C, a significantly reduced water absorption compared to pure PMMA of about 0.32%, but also a higher birefringence (a stress-optic coefficient of 5.2 X 10 , compared with 0.3 X 10 for PMMA and 6.8 x 10 for BPA-PC). 

Another approach uses the reaction of 6-chloro-5-nitropyrimidines with a-phenyl-substituted amidines followed by base-catalyzed cyclization to pteridine 5-oxides, which can be reduced further by sodium dithionite to the heteroaromatic analogues (equation 97) (79JOC1700). Acylation of 6-amino-5-nitropyrimidines with cyanoacetyl chloride yields 6-(2-cyanoacetamino)-5-nitropyrimidines (276), which can be cyclized by base to 5-hydroxypteridine-6,7-diones (27S) or 6-cyano-7-oxo-7,8-dihydropteridine 5-oxides (277), precursors of pteridine-6,7-diones (278 equation 98) (75CC819). 

The parent TMM precursor (1) reacts with tropones (117) to give reasonable yields of the bridged [4.3.1]decanones (118) [43]. Various substituted TMMs also cycloadd to tropone with regioselectivity similar to that of the corresponding [3+2] cases [20, 43]. Addition of MesSnOAc as a co-catalyst also leads to yield improvement [16]. In the case of a phenyl-substituted tropone and a methyl-TMM, performing the reaction under high pressure favors the formation of kinetic products (119) and (120) over the thermodynamic product (121) [11]. 

The nucleophilic alkenoylation of a-phenyl-substituted aldehydes and ketones with (methyl-substituted) [l-cyano-l-(trimethylsilyloxy)-2-propenyl]lithium proceeds with good 1,2-induction to afford the j> i-hydroxy ketones109. 

The kinetic form of the decomposition in various solvents indicates competing unimolecular homolysis of the peroxide link (a) and radical induced decomposition (b). Other diacyl peroxides behave similarly, except that, in the case of acetyl peroxide, induced dceomposition is much less important. More highly branched aliphatic or a-phenyl-substituted diacyl peroxides decompose more readily, partly because induced decomposition is more important again and partly because of the occurrence of decomposition involving cleavage of more than one bond (for a mechanistic discussion of these cases, see Walling et al., 1970). 

In aqueous solution especially, the current yield is distinctly lower furthermore, solubility problems can occur when the salt-deficit method is used. In aqueous solution, a-amino- or a-phenyl substituted carboxylates lead mainly to decomposition products, whilst in dry methanol or methanol-pyridine, coupling products were obtained with a-phenyl- and a-acetylaminocarboxylates [49]. 

A corresponding correlation is obtained for the rate constants of a,a -phenyl substituted alkanes 26 (R1 = C6H5, R2 = H, R3 = alkyl) (see Fig. 1 )41). It has, however, a different slope and a different axis intercept. When both correlations are extrapolated to ESp = 0, a difference of about 16 kcal/mol in AG is found. This value is not unexpected because in the decomposition of a,a -phenyl substituted ethanes (Table 5, no. 22—27) resonance stabilized secondary benzyl radicals are formed. From Fig. 1 therefore a resonance energy of about 8 kcal/mol for a secondary benzyl radical is deduced. This is of the expected order of magnitude54. ... 

The synthesis of novel substituted 6aA4-thia-l,6-diazapentalenes 33 was achieved by a base-induced dimerization of two isothiazolium salts <2001PS(170)29>. It was shown that A -phenyl-substituted isothiazolium salts having active 5-methyl or 5-methylene groups can easily be obtained by reaction of (l-thiocyanatovinylaldehydes and substituted anilines <1995CZ175>. 

The thermal rearrangement of 1,2-dialkynylimidazoles gave intermediate cyclopentapyrazine carbenes 83, which then trapped the solvent (benzene) to give a phenyl-substituted products 84 <06TL353>. 

A palladium catalyst is used in the transformation of a siloxyfuran to a phenyl substituted furanone <00JCS(P1)3350>. Similar products, furan-2(5//)-one derivatives, are afforded through the reaction of tetra-n-butylammonium fluoride with the corresponding substituted 2-siloxyfuran <00S1878>, as well as the oxidation of 3,4-disubstituted furans by singlet oxygen . 

When dimethylgermylene is formed by the decomposition of 8 in the presence of excess styrene, cis- and fraws-l,l-dimethyl-3,4-diphenylgermacyclopentane forms from the apparent cycloaddition of dimethylgermylene to two alkene molecules. This is thought to occur by a stepwise mechanism where dimethylgermylene adds in a concerted fashion to styrene to yield a phenyl-substituted germacyclopropane, in the first step. In a second step, concerted addition of the germacyclopropane to a second styrene molecule has been proposed (Scheme 6). 

The regiochemistry can be controlled by the nature of the substituents. With a tri-methylsilyl-substituted acetylene, the trimethylsilyl groups are placed in a positions of zirconacyclopentadienes with excellent selectivity (Eq. 2.8) [20]. With a phenyl-substituted alkyne, regioselective reactions are usually observed, although in some cases a mixture of two isomers may be formed. 

D.M. Johansson, M. Theander, G. Srdanov, G. Yu, O. Inganas, and M.R. Andersson, Influence of polymerization temperature on molecular weight, photoluminescence, and electroluminescence for a phenyl-substituted poly(p-phenylene vinylenes), Macromolecules, 34 3716-3719, 2001. 

An unusual approach is the isomerization of a methyl-substituted 1,2,3-buta-triene to a vinylallene by stoichiometric deprotonation with wBuLi-TMEDA and reprotonation [83]. With an ether substituent on the butatriene a similar reaction is possible with KOtBu in DMSO [84], while a phenyl-substituted butatriene reacted spontaneously in CHC13 [85]. 

The cobalt mediated homo Diels-Alder reaction of norbomadiene (560) with phenyl acetylene (568a), affording a phenyl substituted deltacyclene, demonstrated the potential of low-valent cobalt complexes as catalysts332. Lautens and coworkers327 extended the scope of this reaction and were able to synthesize a wide range of substituted deltacyclenes from alkynes 568 (equation 164, Table 33). The low-valent cobalt or cobalt(O) species to be used was prepared in situ by reduction of Co(acac)3 with Et2AlCl. Monosubstituted... 

Figure 6.14 Structure of 7-deazaguanine (A), a reduced abasic nucleotide (B), and a phenyl-substituted nucleotide (C).

The activity of Of-carbon alkyl and cycloalkyl substitutions is presented in Table III. These data indicate that the or,Of-dicyclohexyl moiety is very active against bean powdery mildew. Further, the data indicate that the a-cycloalkyl-or-phenyl moieties are not only superior to a-alkyl-a-phenyl substitutions for powdery mildew control, but that they also confer some activity against cucumber anthracnose. Based on these and other data, the a,a-diphenyl substitution was considered to be the best choice. 

The a-phenyl substituted six-membered sulfur-containing material 399 was reduc-tively cleaved using DTBB (5%) as the arene catalyst in THF at —78°C. The resulting intermediate 400 was then reacted with an electrophile followed by hydrolysis, yielding functionalized thiols 401 (Scheme 112) . 

The preparation of A-phenyl-substituted hydroxamic acids 125 in the reaction of formaldehyde with nitrosobenzene to give 124 is strongly catalyzed by Fe + ions, which stabilize the transition states 126 and 127 for the rate-controlling proton transfer from the carbon atom of nitrosocarbinolic cation intermediate 125 leading to the product 128 (Scheme 62) . 

R, R = alkyl, R = GOOCHs) For a-phenyl substituted azoalkanes 20 (R, R = alkyl, R = CsHj ) the relationship between thermal stability and size of the groups R and R is more complex, apparently because the resonance stabilization of the developing radical center at the transition state 23 decreases with increas-... 

Dianions of the above types may not fall into the category of homoenolate in a strictly formal sense. Nevertheless the amide dianion does show a behavior typical of the homoenolate. Thus, the reaction of the isotopically labeled stannylpropionate results in scrambling of the label probably via a cyclopropane intermediate Eq. (47) [44]. As the result of such an equilibration, isomerization of a-methyl and a-phenyl substituted propionate homoenolates may occur to give the thermodynamically more favorable isomers, respectively. 

Oxidation with permanganate588 592 636 637 usually requires the use of a suitable solvent mixture, such as aqueous THF,638 which dissolves both permanganate and the alkene. Better results may be obtained by phase-transfer agents.440 Reaction with tetraalkylammonium permanganate may allow selective cleavage of a phenyl-substituted double bond in dienes.639... 

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