Biphenyl substitution

At this point it was clear that the highest potential for increased activity was by substitution in the 2-position of the biphenyl alcohol. We prepared the sequence of compounds shown in Table 1. Substituents were again chosen to maximize the parameter space covered within the relatively stringent synthetic limitations of the biphenyl substitution pattern. The application of regression analysis to the data for these compounds provided no clear relationship between structure and activity when the parameters in our standard data base were used. The best linear fit was found for B4, the STERIMOL maximum radius. However, the correlation coefficient was only 0.625. 

In view of this background, we developed a new chiral auxiliary to allow for the first time the efficient asymmetric a-alkylation of sulfonamides [90]. After testing some amine auxiliaries mainly based on proline, which did not show high diastereoselectivities, we synthesized the 4-biphenyl-substituted 2,2-dimethyl-l,3-dioxan-5-amine 108 as a new auxiliary. The racemate obtained according to Erlenmeyer s phenylserine synthesis was resolved with tartaric acid to give both enantiomers. 

An examination of the data for substitution in the 2-position of fluorene (Fig. 32) reveals a reasonable correlation. Some scatter is observed but no more than is generally encountered in an application of the Hammett treatment to data covering a wide range of reactivity. Certainly, there is no evidence for a pronounced curvature of the kind found in the related treatment of the data for biphenyl (Figs. 29 and 30). In contrast to substitution in the para position of biphenyl, substitution in the structurally equivalent 2-position of fluorene conforms to the Extended Selectivity Relationship (see, however, p. 147). 

The UV-visible absorption maxima and edges of the various PPV derivatives are summarized in Table 1. PFPV [7] with electron-withdrawing substituent shows a blue-shifted absorption at 410 nm and perfluorinated biphenyl substituted PPFPV [20] shows more blue-shifted absorption at 400 nm. Benjamin et al. [21] have reported that a copolymer composed of the PPV part and the 2,3,5,6-tetrafluoro-PPV part showed a blue-shifted absorption compared with that of unsubstituted PPV. These shifts are explained as being a result of the inductive electron withdrawing properties of the fluorine substitution leading to reduced electron density in the conjugated polymers and leading to an increase in the HOMO-LUMO band gap. 

Decarboxylation of benzoates in the presence of an aryl halide (20, 33, 211) affords the biphenyl substitution products in yields of up to 50% if the medium is an iV-heteroaromatic solvent. The solvent must be dry to avoid reductive dehalogenation (54). If the solvent is dry diglyme or xylene, an ester can be isolated in high yield (54). 

Table 10. Dissociation constants K of biphenyl substituted phenoxyls...

The 50% phenyl-substituted silicone and 30% biphenyl-substituted silicone stationary phases are moderately polar and contain polarizable aromatic rings that exhibit induced dipoles in the presence of dipolar solutes such as alcohols, phenols, amines, nitriles, ketones, and so forth. They give selectivity with-... 

The relatively small perturbation of the triarylmethyl sites by biphenyl substitution allowed for both control of electron localization and exchange coupling. When the triarylmethyl spin sites were adjacent, the exchange coupling was ferromagnetic,... 

Fig. 34 Organic trimer of component spins, 7/2-1/2-7/2, corresponding to pentadecaradical 51. (A)-(F) correspond to spin systems for the configurations with 0-2 antiferromagnetic couplings through the biphenylene coupling units and 0-1 chemical defects at the 4-biphenyl-substituted sites.

The formation of biphenyl-substituted bis-Gp titanium complexes (Scheme 439) has been detected during the synthesis of -biphenyl-bridged bis-Cp derivatives.1050 The synthesis of the bis(tetrahydroindenyl) dichloride (C9H10)TiCl21051 and of [G5H3(l,2-CH2-)J2TiCl2 (n = 4-6) (Scheme 440)1052 have been reported. 

Armesto and his co-workers" have demonstrated that electron-transfer induced cyclization of imines (66) follows the di-jr-methane pathway, via the intermediate radical cation (67), to afford the cyclopropane derivatives (68). The outcome of the reaction is to some extent controlled by the electron-transfer sensitizer used, as can be seen in the reported yields. In the biphenyl substituted example, a cyclopropane derivative (69) is formed in competition with an alter-... 

Frey, S., H.T. Rong, K. Heister, Y.J. Yang, M. Buck and M. Zharnikov. 2002. Response of biphenyl-substituted alkanethiol self-assembled monolayers to electron irradiation Damage suppression and odd-even effects. Langmuir 18 3142-3150. 

Serendipity in the traditional screening approaches is, up to now, one of the main resources for discovering acaricides with novel biochemical and physiological targets [2]. Based on the discovery that fungicidal phenylhydrazide compounds had some acaricidal activity, a synthesis program was initiated in Crompton Co. Research in 1990. From among several hundred carbazate derivatives synthesized and evaluated for acaricidal activity the methoxy-biphenyl-substituted carbazate (bifenazate. Fig. 30.2.1, Table 30.2.1) was selected for development [3]. 

After the discovery that ortho-biphenyl substituted hydrazide compounds [5] had acaricidal activity in the pesticide discovery screen (Table 30.2.3) several hundred - structurally diverse - biphenyl-substituted carbazate analogs were synthesized, and, in an optimization process using a bioassay with the two spotted spider mite (Tetranychus urticae Koch), isopropyl-2-(4-methoxy[l,l -biphenyl]-3-yl) hydrazine carboxylate (bifenazate) [3, 8] was identified as the most advantageous compound. 

Table 30.2.3 Structure-activity relations of ortho-biphenyl substituted hydrazide compounds [9, 10].

In contrast to the ortho-biphenyl-substituted carbazates the isomeric alkyl-meta-biphenyl-carbazates are available in a multistep synthesis, allowing one to introduce different substituents, like alkoxy, alkylthio, alkylsulfonyl, to the pendant phenyl group (Scheme 30.2.1) [12] ... 

Hydroxyphenyl)-4,6-d-p-tolyl-l,3,5-triazine Biphenyl-substituted triazines... 

The tide compounds are obtained in moderate to good yields. While the 3- and 5-biphenyl-substituted derivatives 24 and 25 can be synthesized by applying the same reaction conditions, the synthesis of 1-biphenylsubsti-tuted pyrazoles 26 requires a different set of conditions, most notably dichloromethane as solvent instead of tetrahydrofuran (THF). The 3-biphe-nylsubstituted pyrazoles 25 are generally obtained in the h hest overall yields. In terms of the appHed boronic acid 22, electron-donating, electroneutral, and electron-withdrawing substituents are accepted. 

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