2,2 -Bipyridyl rearrangement

Building blocks, useful for supramolecular or material science, have also been prepared using the Boekelheide reaction. Thus bipyridyl derivative 23 was subjected to the standard sequence of reactions (oxidation, rearrangement, and hydrolysis) to afford the diol 24. 

The first hydration step was promoted by Bronsted acids containing weakly or noncoordinating anions. In the second step, an intramolecular hydrogen transfer in the secondary alcohol was catalyzed by ruthenium(III) salts with chelating bipyridyl-type ligands. The possible complexation of the latter with the diene did not inhibit its catalytic activity in the allylic rearrangements, under acid-catalyzed hydration conditions. 

The well documented oxidation of 1,10-phenanthroline (4) to 2,2 -bipyridyl-3,3 -dicarboxylic acid (53) by alkaline permanganate has been repeated. It is now found that 4,5-diazafluoren-9-one (54) is consistently a coproduct of the reaction in 20% yield.253 This provides a convenient route to this hitherto difficultly accessible compound. The formation of 4,5-diazafluoren-9-one almost certainly occurs by way of the intermediate, but not isolated, l,10-phenanthroline-5,6-dione, which is known to undergo a benzilic acid type rearrangement in the presence of hydroxide ions to give the diazafluorenone. This rearrangement of l,10-phenanthroline-5,6-dione has recently been studied further.115 Under some conditions 5,6-dihydro-5,6-dihydroxy- 1,10-phenanthroline can be isolated with the diazafluorenone. 

A more complex reaction sequence may be responsible for the formation of the products of formal insertion of silylenes into the H—C bonds of carbaldimines110 116. As shown in equation 56, an initial Lewis base or TT-bond adduct can undergo rearrangement to both of the products observed from reactions of diarylsilylenes and pyridine-2-carbaldimines. A common intermediate is suggested by the thermal isomerization of the insertion product to the cycloadduct which can be the exclusive product from addition of a silylene to a 2,2/-bipyridyl (see Section ni.B)117. 

The principal synthetic route to diazafluorenes involves the alkaline oxidation of phenanthrolines, presumed to give initially the rarely isolated 5,6-dione which (i) further oxidizes to a bipyridyl dicarboxylic acid (the main product) or (ii) undergoes a benzilic acid type rearrangement followed by oxidative decarboxylation to give diazafluorenones in moderate yields (Scheme 2) <77JPR959>. The process has been reviewed by Summers <78AHC(22)i>. The yields of 4,5-diazafluorenone have been optimized <73AJC2727>. 

In deference to their biological significance much work has been done on this class of compound a model studies to analyze or mimic the behavior of pyridine nucleotides and bipyridinium herbicides, py ridinium ions (132 Scheme 26) being more susceptible to reduction. Dimerization is a common fate o the neutral radical formed. The most thermodynamically stable product, the 4,4 -bipyridyl species pre dominate, and other dimers can sometimes rearrange to the 4,4 -bipyridyl isomer. Radicals with mere... 

Formation of spiro orthoesters such as 4 is achieved in high yield by reaction of cyclic ketene monothioacetals such as 3 with ethanediol and camphorsulfonic acid <04SL2013>. A variety of substituted epoxy ketones 5 rearrange to the benzodioxoles 6 upon treatment with Bu.,N CN in CHjClj or K1 in acetone <04T3825>. Condensation of phenacyl carbonates 7 with aromatic aldehydes in the presence of MgCClO ), 2,2 -bipyridyl, A-methylmorpholine and molecular sieves gives the trans dioxolanones 8 <04SL1195>. 

Nitropyridine and 4-hydroxypyridine-l-oxide in boiling methanol react to give 7V-(4 -pyridyloxy)-4(l/0pyridone (MI-371), which rearranges to 3,3 -(4,4 -dihydroxy)bipyridyl on heating at 100 in benzene or dioxane. Evidence supports a homolytic fission of the N—0 bond in XII-371 to give a biradical intermediate. ... 

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