2015
DOI: 10.1071/ch15393
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Iridium-Catalyzed Triborylation of 3-Substituted Indoles

Abstract: Readily available 3-substituted indoles undergo a one-pot iridium-catalyzed triborylation at the C2, C5, and C7 sites. 1 H NMR analysis indicates borylation at C2 and C7 occurs first (no monoborylated product is observed), with the third borylation occurring as a separate, distinct step that is sterically directed to C5 by a combination of the substituent at C3 and the boronate at C7. The resulting tetrasubstituted indoles possess a substitution pattern that is cumbersome to prepare using existing methods.

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Cited by 11 publications
(8 citation statements)
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“… [119] With higher stoichiometries of B 2 pin 2 , iterative borylation of 3‐substituted indoles such as 3‐methylindole ( 136 ) can occur, with C−H activation occurring at, successively, C‐2, C‐7, and C‐5 (Scheme 15 g). [120] Formal selective C‐7 mono‐borylation of indole is possible by blocking C‐2 with a labile group, which is subsequently removed. For example, a 2‐silyl substituent can be selectively cleaved using TBAF after having sterically directed borylation to C‐7 (Scheme 15 h).…”
Section: Borylation Of Heteroarenesmentioning
confidence: 99%
“… [119] With higher stoichiometries of B 2 pin 2 , iterative borylation of 3‐substituted indoles such as 3‐methylindole ( 136 ) can occur, with C−H activation occurring at, successively, C‐2, C‐7, and C‐5 (Scheme 15 g). [120] Formal selective C‐7 mono‐borylation of indole is possible by blocking C‐2 with a labile group, which is subsequently removed. For example, a 2‐silyl substituent can be selectively cleaved using TBAF after having sterically directed borylation to C‐7 (Scheme 15 h).…”
Section: Borylation Of Heteroarenesmentioning
confidence: 99%
“…To complete the SAR study, we decided to synthesize and test a triply arylated Trp derivative whose obtention would be accomplished through a convergent synthetic strategy similar to that described above ( Scheme 4 ). The key intermediate in this route was triply arylated Trp derivative 35 , which was obtained through an SMR between the crude organoboron Trp intermediate 34 , 48 bearing three Bpin substituents at the C2/C5/C7 positions, and isophthaloyl bromide. Subsequent removal of the Boc-protecting group afforded amino intermediate 36 .…”
Section: Results and Discussionmentioning
confidence: 99%
“…This desired transformation aligns perfectly with the iridium-catalyzed C-H borylation reaction, 15 the regiochemical outcome of which is reliably dictated by the directing ability of the indole N-H. Subjecting 1 to an iridium-catalyzed C-H borylation using the 3,4,7,8-tetramethylphenanthroline as ligand (Me4Phen) 16,17 gave the 7-borylindole 9 in good yield. A DMAP-assisted 18 Chan-Evans-Lam coupling of 9 with methanol gave the natural product 5,7-dimethoxy-2,4-dimethylindole (3).…”
mentioning
confidence: 90%