Hydroxy group activation

This technology could also be applied for the oxidation of methane (70 °C, 5 Mpa) to formic acid (46% selectivity based on hydrogen peroxide). Another catalyst which can be applied for the direct oxidation of benzene with H202 is the TS-1 catalyst, as described above for propylene epoxidation [41]. Conversion is generally kept low, because introduction of a hydroxy group activates the aromatic nucleus to further oxidation to hydroquinone, catechol and eventually to tarry products [137]. 

Preparative Methods (1) is easily made by cy clization of commercially available A-Cbz-r-serine (4) under modified Mit-sunobu conditions, using a preformed complex of dimethyl azodicarboxylate (DMAD) and Triphenylphosphine (eq 1). The reaction proceeds via hydroxy group activation, and labeling studies show that the 3-hydroxy group is lost in a 4-exo-tet cyclization mechanism. The p-lactone must be separated quickly from the reaction mixture, and a slight excess of DMAD improves the yield because unreacted triphenylphosphine can cause polymerization. The Boc (f-butoxycarbonyl) analog (2) is prepared similarly, and the p-toluenesulfonate (tosylate) salt (3) is synthesized from (2) by acidic cleavage. ... 

Tetra-n-butylammonium triacetoxyborohydride in refluxing benzene reduced aldehydes but not acyclic ketones, the selectivity was demonstrated in competition experiments and keto aldehyde reductions. The more reactive cyclohexanones were reduced only slowly under the same conditions. The limitation of this convenient method is that proximal hydroxy groups activated the reagent enabling the... 

Esters from Carboxylic Acids and Alcohols via Hydroxy Group Activation (HGA)... 

Yoshikoshi recently reported a 1,3-diol fragmentation (Scheme 14a) under mild conditions, where a benzylic hydroxy group activated by the 2,6-dimethoxy-4-methylphenyl group proved to be a remarkably reactive nucleofuge. 

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