Homogeneous [Ru-III(Me(3)tacn)Cl-3]-catalyzed alkene cis-dihydroxylation with aqueous hydrogen peroxide

A simple and green method that uses [Ru(Me(3)tacn)Cl-3] (1; Me(3)tacn = N,N',N ''-trimethyl-1,4,7-triazacyclononane) as catalyst, aqueous H2O2 as the terminal oxidant, and Al2O3 and NaCl as additives is effective in the cis-dihydroxylation of alkenes in aqueous tert-butanol. Unfunctionalized alkenes, including cycloalkenes, aliphatic alkenes, and styrenes (14 examples) were selectively oxidized to their corresponding cis-diols in good to excellent yield (70-96%) based on substrate conversions of up to 100%. The preparation of cis-1,2-cycloheptanediol (119 g: 91 % yield) and cis-1,2-cyclooctanediol (128g, 92% yield) from cycloheptene and cyclooctene, respectively, on the I-mol scale can be achieved by scaling up the reaction without modification. Results from Hammett correlation studies on the competitive oxidation of para-substituted styrenes (rho=-0.97, R=0.988) and the detection of the cycloadduct [(Me(3)tacn)ClRuHO2(C8H14)](+) by ESI-MS for the 1-catalyzed oxidation of cyclooctene to cis-1,2-cyclooctanediol are similar to those of the stoichiometric oxidation of alkenes by cis-[(Me(3)tacn)(CF3CO2)(RuO2)-O-VI](+) through [3+2] cycloaddition (W.-P. Yip, W.-Y. Yu, N. Zhu, C.-M. Che, J. Am. Chem. Soc. 20057 127, 14239).