The studies on transition metal-catalyzed addition reactions of carboxylic acids, alcohols, sulfon-amides, and 1,3-diketones onto olefins toward the development of olefin hydration using transition metal catalysts were described. Both intramolecular cyclizations and intermolecular additions successfully proceeded to give the corresponding adducts under mild condition. For example, 2-allylphenol was treated in the presence of 1 mol% of (Cp*RuCl2)(2)/4AgOTf in benzene at reflux to afford 2,3-dihydrobenzofuran in 95% yield. Ru-xantphos catalysts showed high catalytic activities on the addition of 2-phenylbenzoic acid, 2-phenylethanol, and tosylamide with 4-allylanisole to afford the corresponding addition products in 95%, 78%, and 78% yields, respectively.