Alkylbenzene side chains are oxidized at the benzylic position when treated under heterogeneous conditions with permanganate adsorbed on a solid support. The products are alcohols if the benzylic carbon is tertiary, or ketones if it is secondary. Carbon-carbon bond cleavage, which usually occurs when these same compounds are oxidized by permanganate under homogeneous conditions, does not occur. A unique selectivity is observed for the oxidation of derivatives of indane, 1, and tetralin, 2, in which one of the methylenes is replaced by an oxygen. If the oxygen is in the α-position, no reaction occurs; if it is in the β-position, good yields of the corresponding lactone are obtained. A mechanism consistent with the observed selectivity has been proposed.