Iridium‐Catalyzed Annulation Reactions of Thiophenes with Carboxylic Acids: Direct Evidence for a Heck‐type Pathway

Abstract

The functionalization of thiophenes is a fundamental and important reaction. Herein, we disclose iridium-catalyzed one-pot annulation reactions of (benzo)thiophenes with (hetero)aromatic or α,β-unsaturated carboxylic acids, which afford thiophene-fused coumarin-type frameworks. Dearomatization reactions of 2-substituted thiophenes with α,β-unsaturated carboxylic acids deliver various thiophene-containing spirocyclic products. The occurrence of two interconnected reactions provides direct evidence for a Heck-type pathway. The mechanistic scenario described herein is distinctly different from the S Ar and concerted metalation-protodemetalation (CMD) pathways encountered in the well-described oxidative C-H/C-H cross-coupling reactions of thiophenes with other heteroarenes.

Recent Development on Cp*Ir(III)‐Catalyzed C−H Bond Functionalization

“…The authors proposed that this oxidative coupling of aryl or unsaturated acids with thiophenes might proceed via a Heck‐type pathway, which is different from the commonly adopted S E Ar or CMD (concerted metalation protonation) pathways in C−H arylation with heterocycles (Scheme ).…”

“…With their continuous research interest for the development of efficient methodologies for C−H/C−H coupling with thiophenes, You disclosed in 2018 a Ir(III)‐catalyzed oxidative annulation reactions of thiophenes with carboxylic acids, providing a rapid access to fused coumarins . With α,β‐unsaturated carboxylic as acids substrates in this oxidative coupling with thiophenes, dearomatization reactions took place to give lactone‐derived spirocyclic products.…”

Copper-catalyzed remote C–H arylation of polycyclic aromatic hydrocarbons (PAHs)

“…The direct C7−H arylation of 1-naphthoic acid derivatives is undoubtedly a more effective route for the synthesis of 7-arylnaphthalene derivatives. Although the transition metal-catalyzed C2−H and C8−H arylations of 1-naphthoic acid derivatives have been widely reported, the studies on their C7−H arylation remain rare [18][19][20][21][22][23][24][25]. Our group has recently reported F + reagent-promoted Pd-catalyzed C7-H arylation of 1-naphthamides, but this method still suffers from a few disadvantages (Scheme 1) [26].…”

Lewis acid-assisted Ir(iii) reductive elimination enables construction of seven-membered-ring sulfoxides

“…[11][12][13][14][15] In contrast, the use of thirdrow transition metals in catalytic elaboration of C-C bonds from C-H bonds appears to have fallen off signicantly. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Iridium complexes have been shown to be highly active for stoichiometric C-H bond activation, while the relatively stable metallacyclic Ir(III) intermediates usually hamper their catalytic turnovers in the Ir(III)-catalyzed C-C bond forming reactions (Scheme 1a). [32][33][34] The main problem lies in the reductive elimination step furnishing C-C bond formation, which is identied as the bottleneck in the catalytic cycle.…”