10.1021/ol302767w r XXXX American Chemical Society ORGANIC LETTERS XXXX Vol. XX, No. XX 000–000 Intramolecular Dehydrogenative Coupling of sp 2 CÀH and sp 3 CÀH Bonds: An Expeditious Route to 2‑Oxindoles Santanu Ghosh, Subhadip De, Badrinath N. Kakde, Subhajit Bhunia, Amit Adhikary, and Alakesh Bisai* Department of Chemistry, Indian Institute of Science Education and Research (IISER) Bhopal, MP-462 023, India alakesh@iiserbhopal.ac.in Received October 8, 2012 ABSTRACT An intramolecular-dehydrogenative-coupling (IDC) using “transition-metal-free” oxidation conditions has been achieved to synthesize a variety of 2-oxindoles bearing an all-carbon quaternary stereogenic center at the benzylic position. The methodology involves a one-pot C-alkylation of β-N-arylamido esters (3, 6) with alkyl halides using potassium tert-butoxide concomitant with a dehydrogenative coupling. A radical-mediated pathway has been tentatively proposed for the oxidative process. Efficient strategies to convert CÀH bonds directly to other functionalities remains an important goal of modern synthetic organic chemistry. 1 In this context, construction of carbonÀcarbon (CÀC) bonds via the oxidative cross- coupling of two carbonÀhydrogen (CÀH) bonds has gained intense interest resulting in the development of numerous new synthetic methods. 2À4 Recently, an intramolecular oxidative coupling (intramo- lecular dehydrogenative coupling, IDC) of Csp 2 ÀH and Csp 3 ÀH in the context of 2-oxindole synthesis was reported independently by Kundig 5 and Taylor 6 in the presence of Cu(II) complexes (Scheme 1). These pioneering efforts led to the synthesis of a wide range of 2-oxindoles 7 bearing all- carbon quaternary stereocenters at the benzylic position. 8 (1) (a) Dyker, G., Ed. Handbook of CÀH Transformations: Applica- tions in Organic Synthesis; Wiley-VCH: Weinheim, 2005; Vol. 2. (b) Stuart, D. R.; Fagnou, K. Science 2007, 316, 1172. (c) Ashenhurst, J. A. Chem. Soc. 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