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제113회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Unprecedented C2-Olefination of N-Substituted Indole and Pyrroles via Rh-catalyzed oxidative C-C bond formation and C-N bond cleavage

2014년 2월 13일 17시 00분 56초
ORGN.P-802 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
4월 16일 (수요일) 16:00~19:00
저자 및
신영미*, 박지혜, 한상일
성균관대학교 약학과, Korea
The indole nucleus is a ubiquitous structural motif found in bioactive natural products, pharmaceuticals, functional materials, and agrochemicals. Thus the efficient synthesis and functionalization of indoles have been of considerable interest in organic and medicinal chemistry. In particular, transition-metal-catalyzed cross-coupling of indoles and aryl halides is one of the most sustainable protocols for the functionalization of indoles. Since the pioneering efforts of Fujiwara and Moritani, remarkable progress has been made on the oxidative Heck coupling between indoles and olefins under palladium catalysis via a twofold C-H bond cleavage. Due to the electrophilic nature of the organometallic species involved in the coupling reaction, the reaction occurs preferentially at the more electron-rich C3 position of the indole ring. Therefore, the highly selective C2-olefination of 2,3-unsubstituted indoles has been an intensive research area to override the inherent selectivity of indoles. For instance, Gaunt described the regioselective Pd-catalyzed intermolecular C2- or C3-alkenylation of free (NH)-indoles by employing different solvents and additives. Satoh and Miura disclosed the Pd(II)- catalyzed C-H alkenylation and subsequent decarboxylation protocol of indole-3-carboxylic acids to afford exclusively C2-alkenylated indoles, where the carboxyl group blocks the C3-position and acts as a removable directing group. Recently, Carretero reported the highly efficient Pd-catalyzed C2-selective olefinations of indoles and pyrroles assisted by a removable N-(2-pyridyl)sulfonyl group. In contrast to the vast majority of documents on the palladium-catalyzed olefinations, the indolic C-H olefinations using rhodium or ruthenium catalysts, which often allow higher selectivities and broad substrate scope, have been much less explored. For example, Glorius first reported a single example of Rh-catalyzed C2-olefination of N-acetyl indoles. Prabhu demonstrated Ru-catalyzed oxidative C2-alkenylation of indoles using the N-benzoyl directing group. Recently, Li and Wang and Song, respectively, reported Rh(III)- and Ru(II)-catalyzed oxidative couplings between indoles containing a N,N-dimethylcarbamoyl group and olefins to afford C2-alkenylated indoles In conclusion, we developed a novel strategy for the formation of C2-functionalized free (NH)-indoles and free (NH)-pyrroles via the rhodium(III)-catalyzed oxidative alkenylation of N-arylcarbamoyl indoles and pyrroles with olefins and subsequent cleavage of a protection group. Further applications to the synthesis of biologically active compounds and a more detailed mechanistic investigation are in progress.