Oxindoles metal-free synthesis

The reaction of A-arylacrylamides and simple alcohols in the presence of 70% aqueous solution of TBHP leads to metal-free synthesis of 3,3-disubstituted oxindoles. A series of hydroxyl-containing oxindole derivatives could be prepared using this method. The reaction is proposed to proceed through an oxidative radical cyclization mechanism and shows excellent functional group tolerance." ... 

J. Lv, D. Zhang-Negrerie, J. Deng, Y. Du, K. Zhao, Metal-free synthesis of 2-oxindoles via PhI(OAc)2-mediated oxidative C-C bond formation, J. Org. Chem. 79 (2014) 1111-1119. 

Additional examples of synthetic applications of hypervalent iodine-induced heterocyclizations include the following the metal-free one-pot synthesis of 2-acylbenzothiazoles by oxidative cyclization of multiform substrates [434], iodine(III)-mediated tandem oxidative cyclization for construction of 2-nitrobenzo[ ]furans [435], hypervalent iodine mediated oxidative cyclization of o-hydroxystilbenes into benzo- and naphthofu-rans [436], PhI(OCOCF3)2-mediated synthesis of 3-hydroxy-2-oxindoles and spirooxindoles from anilides [437], synthesis of isoxazoles by hypervalent iodine-induced cycloaddition of nitrile oxides to alkynes [438],... 

Hypervalent iodine reagents have successfully been employed in the oxidative functionalization of enolizable carbonyl compounds over the years [6]. This methodology has allowed the construction of diverse C-C bonds in the context of heterocychc synthesis and has enriched the otherwise rare repertoire of such chemistry. Zhao, Du, and coworkers [37] have recendy realized a metal-free PIFA-mediated synthesis of 3-hydroxy-2-oxindoles 34 and spirooxindoles 35 starting from anilide derivatives 33 (Scheme 8 (1)). These processes showcase an oxidative cross coupling between an aromatic carbon and a pendant aliphatic carbon, followed by further oxidative hydroxylation or spirocycUzation. Later, the authors extended the same concept to achieve C(sp )-C(sp ) bond formation, where anilide derivatives possessing terminal enol functionality underwent PIDA-... 

Antonchick s group [68] developed a PIFA-mediated unprecedented and efficient azidoarylation of alkenes which occurs under mild and metal-free reaction conditions and provides a general approach to the synthesis of biologically interesting 2-oxindoles 93 (Scheme 22). In order to demonstrate the potential of the methodology, the authors performed several post-synthetic transformations of the... 

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