Cationic Cobalt(III) Catalyzed Indole Synthesis: The Regioselective Intermolecular Cyclization of N‐Nitrosoanilines and Alkynes

Abstract

The unique regioselectivity and reactivity of cobalt(III) in the direct cyclization of N-nitrosoanilines with alkynes for the expedient synthesis of N-substituted indoles is demonstrated. In the presence of a cobalt(III) catalyst, high regioselectivity was observed when using unsymmetrical meta-substituted N-nitrosoanilines. Moreover, internal alkynes bearing electron-deficient groups, which are almost unreactive in the [Cp*Rh(III)]-catalyzed system, display good reactivity in this transformation.

Mild C−H/C−C Activation by Z‐Selective Cobalt Catalysis

“…[8] Therecent years have witnessed increasing interest in the use of naturally abundant 3d transition metal catalysts for CÀH functionalizations. [9] Particularly,c obalt(III) complexes have emerged as versatile tools, [10] with key contributions by Matsunaga/Kanai, [11] Ellman, [12] Chang, [13] Glorius, [14] Shi, [15] Jiao, [16] and Ackermann, [17] among others. [18] As part of our research on base-metal-catalyzed C À Hactivation, [19] we have now developed the first cobalt-catalyzed CÀH/CÀCfunctionalization.…”

Cp*CoIII‐Catalyzed C(sp3)−H Bond Amidation of 8‐Methylquinoline

“…[4][5][6][7][8][9][10][11] In particular, Glorius, [5] Ackermann, [6] Ellman, [7] Chang, [8] Sundararaju, [9] Cheng, [10] and others [11] have demonstrated the uniquer eactivityo fC p*Co III for C(sp 2 )ÀHb ond functionalization. But to the best of our knowledge,C p*Co III catalysth as rarelyb een employed for C(sp 3 )ÀHb ond activation/functionalization.…”

Microwave‐Assisted Rapid One‐Pot Synthesis of Fused and Non‐Fused Indoles and 5‐[18F]Fluoroindoles from Phenylazocarboxylates

“…Due to their importance, new synthetic methods are perpetually developed . Recently published strategies comprise the assembly of the indole moiety through cobalt‐,– rhodium‐,, or palladium‐catalyzed– reactions of such diverse starting materials as nitrones, azo esters, hydrazides,, nitrosoanilines, enamines, or imines . In addition to these developments, the classical Fischer indole synthesis is also constantly improved and remains attractive in medicinal chemistry and in natural products synthesis…”