Methoxy radical recombination

However, among reactions of radical recombination, Ifaere are isuch reactions for which exp ko but t), i.e., they are not limited by the translatory diffusion of reactants but depend, nevertheless, on the molecular mobility of the environment. They were named pseudo-diffusion reactions. They are the recombination of 2,6-disubstituted phenoxyls, whose substituents are phenyl, methoxy, and rer/-butyl groups. They are characterized by proportionality but xp is by 1, 2 or 3... 

Thermolysis of 2-acetoxy-2-methoxy-5,5-dimethyl-A3-l,3,4-oxadiazoline affords acetoxy(methoxy) carbene.60 The thermal rearrangement of acetoxy(methoxy) car-bene to methyl pyruvate was studied by DFT at the B3PW91/6-31G(d,p) level. The conformation of the carbene was considered, as were competing fragmentations to radical pairs. The authors concluded that the reaction is a concerted 1,2-migration rather than a fragmentation-recombination process. 

The rearrangement is found to be of intramolecular nature. The radical pair remains in the solvent cage and their recombination in the cage affords the acyl migration products, while hydrogen abstraction by the phenoxy radical from the solvent leads to the formation of phenol as by-product. When the reaction of phenyl acetate was carried out with deuterated phenol in methanol, the major products were ortho- and para-hydroxy acetophenones and phenol. Only trace amounts of crossover products were obtained [42]. The presence of methoxy substiment at meta- and para-positions increases the yield of ortho-Vries product [43]. For example, 39 gives 40. 

Suggs and Jun had determined that a homolysis-recombination mechanism was operative in the thermolysis of (S)-8-quinolinyl a-methoxybenzyl ketone 17 (see Scheme 7). An analogous cage-escape crossover experiment was performed on 3-methoxy-aiyl derivative 45 with 6-methyl-quinolinyl derivative 52 in order to probe the nature of the intermediates (Scheme 19). Both substrates underwent complete conversion to their respective product (53 and 54) without detection of crossover products 55 or 33. It is therefore unlikely that this transformatiOTi proceeds through a radical mechanism. 

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