C3-Alkylation of indoles and oxindoles by alcohols by means of borrowing hydrogen methodology

Transition metal-catalyzed C3-alkylation of indoles and oxindoles with nonderivatized alcohols, by means of borrowing hydrogen (BH) activation of the alcohol substrates, avoids the use of environmentally unfriendly alkylating agents. Only water is formed as the byproduct, thus making the BH process atom-economical and environmentally benign. Diverse homogeneous and heterogeneous transitionmetal catalysts, indoles and oxindoles, and nonderivatized alcohols can be used for this transformation, hence rendering the BH process promising for replacing those procedures that use traditional alkylating agents. Although some earlier literature is discussed, this review mainly covers the literature published since 2015. (C) 2020 Elsevier Ltd. All rights reserved.