Ir-catalyzed borylation of 2-substituted indoles selectively yields 7-borylated products in good yields. N-Protection, required for previous functionalizations of 2-substituted indoles, is unnecessary.
Ir-catalyzed C–H borylation is found to be compatible with Boc protecting groups. Thus, pyrroles, indoles, and azaindoles can be selectively functionalized at C–H positions β to N. The Boc group can be removed on thermolysis or left intact during subsequent transformations.
Indole derivatives R 0140Ir-Catalyzed Functionalization of 2-Substituted Indoles at the 7-Position: Nitrogen-Directed Aromatic Borylation. -The Ir-tBu-bipy-catalyzed reaction of N-unsubstituted 2-substituted indole derivatives (I) with pinacolborane proceeds regioselectively to afford the 7-borylated products (III) in good yields. When the 2-position is unsubstituted as in indole (VI), 2,7-diborylated products are formed. The 7-borylation products can be applied directly in the Suzuki cross-coupling reaction to give 7-arylindoles (V). -(PAUL, S.; CHOTANA, G. A.; HOLMES, D.; REICHLE, R. C.; MALECZKA*, R. E. J.; SMITH, M. R. I.; J. Am. Chem. Soc. 128 (2006) 49, 15552-15553; Dep. Chem., Mich. State Univ., East Lansing, MI 48824, USA; Eng.) -Mischke 16-113
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