Aliphatic C-H functionalization at indole 2α-position mediated by acyloxythionium species 1 generated from sulfoxide and acid anhydride has been developed. The combination of sulfoxide and TFAA with O-, N- and C-nucleophiles enabled introduction of various substituents in a one-pot procedure. Especially on utilizing DMSO, the combination provided a practical and efficient method for the synthesis of a wide range of 2α-substituted indoles.
The one-pot 2-and 3-functionalization of 2,3-disubstituted indoles using a hypervalent iodine reagent has been developed. The substitution at the 2-position of indoles took place using phenyliodinebis(trifluoroacetate) with oxygen and carbon nucleophiles in moderate yields. The combination of iodosobenzene and trimethylsilyl azide afforded 3-azide derivatives preferentially.The latter reaction was applied to other 2,3-disubstituted indoles.Recently, Ishibashi's group revealed the combination of phenyliodine diacetate (PIDA) and tetrabutylammonium iodide (TBAI) reacted with tetrahydrocarbazoles to give 2-acetoxy derivatives. 6 Alternatively, Du Bois and co-workers developed that the reaction of tetrahydrocarbazoles using imino 3 -iodanes with a rhodium catalyst affords 2-and 3-amino derivatives. 7Recently, we developed the concise 2-functionalization of indole derivatives using a thionium species generated from DMSO-TFAA (Scheme 1). 8
The hypervalent iodine-mediated one-pot C-H functionalization at the 2-or 3-position of indole derivatives is studied. Ph-I(N 3)2 needed for the introduction of the azido group can be prepared in situ from iodosobenzene and trimethylsilylazide. -(HIGUCHI, K.; KAWASAKI*, T.; INABA, M.; NAGANUMA, A.; ISHIZAKI, T.; TAYU, M.; Heterocycles 89 (2014) 9, 2105-2121, http://dx.doi.org/10.3987/COM-14-13065 ; Meiji Pharm. Univ., Kiyose, Tokyo 204, Japan; Eng.) -M. Bohle 09-152
A new procedure for the C-H functionalization at indole 2α-position is developed using a combination of dimethyl sulfoxide, trifluoroacetic anhydride, and a nucleophile. This method allows the synthesis of various substituted indoles, which are useful substrates for the synthesis of natural products and biologically active compounds. -(TAYU, M.; HIGUCHI*, K.; INABA, M.; KAWASAKI, T.; Org. Biomol. Chem. 11 (2013) 3, 496-502, http://dx.doi.org/10.1039/c2ob26944a ; Meiji Pharm. Univ., Kiyose, Tokyo 204, Japan; Eng.) -M. Zastrow 22-123
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