Biphenyl oxidative rearrangement

Scheme IS dq>icts a high yield, general method for specific ortho allgriation of polycyclic aromatic hydrocarbons. In this example, biphenyl is subjected to reductive methyladon followed by oxidative rearrangement with trityl tetrafiuoioborate to give 2-methylbipbenyl. In unsymmetrical substrates the regioselectivity is poor, phenanthiene gives a 3 2 mixture of 4-methyl- and 1-mediyI-phenanlhrene.

Acid chlorides are reacted with diazomethane to yield the diazoketone which upon reaction with silver oxide rearranges to the next higher homolog of the acid. Biphenyl-2-acetic acid is produced in 86% by the method described below [18]. 

Although cyclic azoalkanes are well known as biradical precursors [159] they have been used as 1,2- and 1,3-radical cation precursors only recently [160-164]. Apart from the rearrangement products bicyclopentane 161 and cyclopentene 163, the PET-oxidation of bicyclic azoalkane 158 yields mostly unsaturated spirocyclic products [165]. Common sensitizers are triphenyl-pyrylium tetrafluoroborate and 9,10-dicyanoanthracene with biphenyl as a cosensitizer. The ethers 164 and 165 represent trapping products of the proposed 1,2-radical cation 162. Comparison of the PET chemistry of the azoalkane 158 and the corresponding bicyclopentane 161 additionally supports the notion that the non-rearranged diazenyl radical cation 159 is involved (Scheme 31). 

Rearrangement to acids is accomplished by adding a dioxane solution of diazoketone to a suspension of silver oxide in warm aqueous sodium thiosulfate solution. Examples include biphenyl-2-acetic acid (86%), ° 1-ace-naphthylacetic acid (64%), decane-1,10-dicarboxylic acid (72%), and o-bromophenylacetic acid (63%). ... 

The reactions of cytochrome P450cam with aryldiazenes (ArN=NH) yield cr-bonded iron-aryl complexes, whose oxidation causes regioselectivc migration of the aryl group from the iron to the porphyrin nitrogens. The influence of high pressure on the formation and rearrangement of these Fe-aryl complexes was studied. The aryls are stable at atmospheric pressure but decompose in a pressure-dependent manner at pressures above 1,500 (Fe-phenyl) or 2,500 bar (Fe-(2-naphthyl) or Fe-(/>-biphenyl)) under formation of the A-aryl protoporphyrin adducts. ... 

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