A Hydride-Free Approach to the Chemoselective Reduction of 3-Phenacylidene-2-oxindoles Using Thiourea Dioxide

A mild and chemoselective protocol for the reduction of 3-phenacylidene-2-oxindoles using thiourea dioxide as a hydride-free reducing agent is described. The reaction proceeds smoothly under simple conditions and selectively reduces activated C═C bonds without affecting other sensitive functional groups. A broad range of substituted substrates is compatible with the methodology, providing the corresponding reduced products in good to excellent yields. The operational simplicity, high chemoselectivity, and functional group tolerance make this approach a practical alternative to the reduction of activated olefins.