Pyridils

Pyridazinotriazole, iV-amino-oxidation, 5, 109-110 Pyridazinyl ketones, 3, 32 Pyridazinyl sulfides quaternization, 3, 18 2,2 -Pyridil... 

Cationic bis(oxazoline) and pyridil-bis(oxazoline) Cu(ll) and Zn(ll) Lewis-acid catalysts. A comparative study in catalysis of Diels-Alder and aldol reactions [101]... 

Fig. 33 Microwave-assisted fluorous Ugi condensations. Reagents and conditions a MeOH, MW 100°C, 10-20 min b TFA-THF, MW 100 °C, 10-20 min. R = Ph, furyl, 3-Me-pyridil, i-Bu, MeSC2H4, PhC2H4 R = t-Bu, cylohexyl. Bn or Bu, m-xylU...

It proves possible to anchor catalysts of H2 evolution to the outer and inner surface of the vesicle membrane. These catalysts are finely dispersed (10-20 A in diameter) metal Pt or Pd particles formed via reduction of appropriate salts in vesicle suspension (see [15, 16] and refs, therein). Among the viologen-type electron carriers a promising one is p-bis (1,2,5-triphenyl-4-pyridil)benzene which possesses reduction potential low enough for water reduction at neutral pH. Recently, using this mediator we succeeded in H2 evolution conjugated with PET... 

Figure 2.4 Redox-active building blocks used in LbL self-assembly. PAH-Os Osmium pyridil-bipyridil modified poly(allylamine) [28,58, 69, 72, 148, 150-154, 184, 185, 191, 203-205] ...

Oxidation of the pyridoins, e.g. with iodine, gives the corresponding a-diketones. The significant electron withdrawal exerted by the 7r-deficient heterocyclic system on carbonyl groups at the a- and y-positions can be demonstrated in the behaviour of the diketones under benzilic acid rearrangement conditions. Whereas 3,3 -pyridil (73) gives a normal... 

A benzilic acid rearrangement can be achieved with 2,2 -pyridil and with the quinoline analogues (75) under mild conditions by using methanolic nickel(II) or cobalt(II) acetates. The product acid is isolated as a metal complex (Scheme 71) (69AJC1439). 

Yoshida and co-workers have reported on the use of alkenyldimethyl(2-pyridil)silanes as versatile platforms for olefin synthesis.The combination of Mizoroki-Heck-type coupling and Hiyama cross-coupling provided a diverse range of stereodefmed polysubstituted olefins. 

Another elegant approach to alkyl- and aryl-substituted quino-lizines involves the condensation of a-picolinium salts carrying an active methylene group on the nitrogen atom with suitable a-diketones. Westphal et al,11 have reacted 1,2-diketones, e.g. diacetyl, benzil, furil, and pyridil, with 2-methyl-A-carbethoxymethylpyridinium halides in the presence of weak bases such as dibutylamine or sodium bicarbonate and obtained the corresponding 2,3-disubstituted quino-lizinium halides [Eq. (3)]. Spontaneous hydrolysis and decarboxylation... 

Reduction of ketones other than 48 to dimers has been examined. Ethyl pyridyl ketone (51) gave a poor yield of the corresponding pinacol (52).79 Pinacols can also be made from crossed coupling of ketones with 3-(48).80 Finally, a study of the radical anions formed from the isomeric benzoylpyr-idines (53) was done, and the rates of rotation of the pyridyl ring were determined.81 The mechanism of reduction of the oxime and thiosemicar-bazone derivatives of 53 was determined by voltammetry techniques.82 The monoimine derivative of the pyridil 54 was reduced to the a-amino ketone 55 (Scheme 18).83 Unsaturated pyridyl ketones and heteroaryl pyridyl ketones have also been studied by voltammetry.84,85... 

Figure 8-43. In the case of complexes of 2,2 -pyridil, the benzilic acid rearrangement may be followed and complexes of the intermediate may be isolated.

The oxidation of the metal complexes of l,10-phenanthroline-5,6-quinone is thought to proceed in a similar manner, with the first step being a benzilic acid rearrangement. Rearrangements of this type may also be followed directly in nickel(u) and cobalt(m) complexes of 2,2 -pyridil. The first step of the reaction involves nucleophilic attack on an O-bonded carbonyl group to form a hydrate, followed by a benzilic acid rearrangement. In this case, the benzilic acid rearrangement products may be isolated as metal complexes (Fig. 8-43). 

ZnMPyP4+ — meso-tetra(iV-methyl-4-pyridinium)porphyrinatozinc(II) ZnC18TMPyP3+andMgC18TMPyP3+ — mcso-tris(iV-methyl-4-pyridil)... 

The reaction mechanism of the very efficient bis(imino)pyridil complexes of iron and cobalt [2,6-(CMe=N(2,6-i-Pr2C6H3))2C5H3N]MCH3+ (M=Fe, Co) has been analyzed computationally [42-44]. The overall mechanism is similar to that depicted above for other systems, but there are some significant... 

The generality of the rearrangement is further illustrated by the reaction of 2,2 -furil with hydroxide ion in dry ether (Table 1). Likewise, 2,2 -pyridil is rearranged in hot methanol solution (40 min) to give the sodium salt of 2,2 -pyridilic acid (86%). Acidification, however, affords bis(2-pyridyl)methanol by decarboxylation since 2,2 -pyridilic acid (16) is structurally similar to a -keto acid. Benzilic rearrangement of 2,2 -pyridil with methanolic nickel(ll) and cobalt(II) acetates results in the formation of metal complexes of 2,2 -pyridilic acid (17 92%). A plausible mechanism is summarized in Scheme 4. Rearrangement is also observed with 2,2 -quinaldil, but benzil, 2,2 -furil or 1-phenyl-2-(2 -pyridyl)ethane-1,2-dione are not susceptible to these metal template reactions. 

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