| Many natural products have the skeletons of indoles, and they have a wide range of biological activities. Rhodium(Ⅲ)-catalyzed C-H activation has become more and more popular in construction of the skeletons of indoles due to its broad functional group tolerance and high reaction activity and selectivity, in which area a variety of researches are on the way.In this context, we have done the following two related work:1) We report herein a new strategy of the Rh(Ⅲ)-catalyzed redox-neutral C7-selective C-H activation/annulation of indolines to rapidly access various privileged 1, 7-fused indolines, by utilizing an oxidizing-directing-group. For example, a Rh(Ⅲ)-catalyzed redox-neutral C7-selective C-H fuctionalization of indolines with aryl alkynes is described to directly access 7-membered 1, 7-fused indolines. Moreover, an unprecedented intramolecular addition of an alkenyl-Cp*Rh(Ⅲ) species to a carbamoyl moiety occurred to give 1H-pyrroloquinolinones when employing alkyl alkynes. Additionally, an efficient Rh(Ⅲ)-catalyzed redox-neutral C7-selective C-H activation/alkenylation/aza-Michael addition of indolines is also developed to give 6-membered 1, 7-fused indolines. The advantages of these processes are: 1) mild and simple reaction conditions; 2) no need for an external oxidant; 3) broad scope of substrates; 4) valuable 6- or 7-membered 1, 7-fused indolines as products.2) The Rh(Ⅲ)-catalyzed [3+2] C-H cyclization of aniline derivatives and internal alkynes represents a useful contribution to straightforward synthesis of indoles. However, there is no report on the more challenging synthesis of pharmaceutically important N-hydroxyindoles and 3H-indole-N-oxides. Herein, we report the first Rh(Ⅲ)-catalyzed [4+1] C-H oxidative cyclization of nitrones with diazo compounds to access 3H-indole-N-oxides. More significantly, this reaction proceeds at room temperature and has been extended to the synthesis of N-hydroxyindoles and N-hydroxyindolines. |
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