Sandmeyer hydroxylation

Hanson, P., Rowell, S. C., Walton, P. H., Timms, A. W. Promotion of Sandmeyer hydroxylation (hemolytic hydroxydediazoniation) and hydrodediazoniation by chelation of the copper catalyst bidentate ligands. Org. Biomol. Chem. 2004, 2, 1838-1855. 

The diazonium salts usually decompose when warmed with water to give a phenol and nitrogen. When treated with CuCl, CuBr, KI, the diazo group is replaced by chlorine, bromine or iodine respectively (Sandmeyer reaction). A diazonium sulphate and hydroxyl-amine give an azoimide. The diazonium salt of anthranilic acid (2-aminobenzoic acid) decomposes to give benzyne. ... 

Ciprofibrate (48), a more potent lipid-lowering agent clofibrate, is prepared from Simmons-Smith product by Sandmeyer replacement of the amino group by a hydroxyl via the diazonium salt. Phenol undergoes the Reimer-Thiemann like process common to these agents upon alkaline treatment with acetone and chloroform to complete the synthesis of ci profib-rate (48). 

In addition to conversion of existing amino groups to other amino groups, the amino groups also can be replaced by halogen or hydroxyl substituents by diazo-tization followed by the Sandmeyer reaction. 

Modification of substituents in purines generally follows patterns which are similar to substituent modification in typicfd aromatic S5rstems. These include interconversion of hydroxyl, thiol, halogeno, amino and similar groups, and Sandmeyer type reactions involving primary amines although isolation of stable diazonium salts is rarely possible. In addition, transformations and reactions of carboxylic acid derivatives follow standard patterns. 

The Sandmeyer reaction is not only useful for the preparation of arylbromides. The Boger group used a Sandmeyer reaction to install both a hydroxyl and chloro substituent in their synthesis of the teicoplanin aglycon (29). Diazotization of 25 followed immediately by hydroxylation with cuprous oxide (halide-free/radical conditions) fiimished phenol 26 in excellent yield, even with several sensitive functionalities present in the molecule. Several steps were then required to convert 25 into aniline 27. At this point, a Sandmeyer chlorination proceeded in moderate yield to furnish the aryl chloride 28. This particular reaction is noteworthy, as the reaction proceeded well, in the presence of a variety of functional groups, many of which were unprotected. 

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