Rh(III)- and Ir(III)-Catalyzed C–H Alkynylation of Arenes under Chelation Assistance

Abstract

An efficient Rh(III)- and Ir(III)-catalyzed, chelation-assisted C-H alkynylation of a broad scope of (hetero)arenes has been developed using hypervalent iodine-alkyne reagents. Heterocycles, N-methoxy imines, azomethine imines, secondary carboxamides, azo compounds, N-nitrosoamines, and nitrones are viable directing groups to entail ortho C-H alkynylation. The reaction proceeded under mild conditions and with controllable mono- and dialkynylation selectivity when both mono- and dialkynylation was observed. Rh(III) and Ir(III) catalysts exhibited complementary substrate scope in this reaction. The synthetic applications of the coupled products have been demonstrated in subsequent derivatization reactions. Some mechanistic studies have been conducted, and two Rh(III) complexes have been established as key reaction intermediates. The current C-H alkynylation system complements those previously reported under gold or palladium catalysis using hypervalent iodine reagents.

Substrate‐Directed C‐H Functionalization of 2‐Aryl Pyridines by Transition Metal Complexes

“…[37] Ir(III) was also reported to be equally effective for this conversion. 2-Aryl pyridinesbearing both electron-donating and electron-withdrawing substituents on aromatic ring gave the products in good yields.…”

Alkynylation with Hypervalent Iodine Reagents

“…In this case, the transformation could be also extended to olefins, 21 giving -disubstituted products containing either a benzene ring, a heterocycle or an alkene. Li and co-workers reported a very complete study on the C-H alkynylation of arenes using TIPS-EBX 52 and either rhodium or iridium catalysts (Scheme 2.22, C [130]). Using a rhodium(III)-Cp* catalyst activated by zinc triflate, a broad range of heterocycles such as pyridine, pyrimidine or pyrazole could be used as directing groups (C1).…”

Rh(III)- and Ir(III)-Catalyzed C–C Bond Cross Couplings from C–H Bonds

“…A valuable solution to these obstacles was found by discovering that hypervalent iodine reagents can be used as a powerful electrophilic alkyne source. The research group of Loh and slightly later the groups of Li and Glorius discovered independently that a large panel of aromatic and vinylic substrates undergoes an extremely mild alkynylation with 1-[(triisopropylsilyl)ethynyl]-1, 2-benziodoxol-3(1H )-one (TIPS-EBX) using [Cp*Rh(III)] catalyst (Scheme 11) [127][128][129][130]. Importantly, as this reaction does not require an addition of an external oxidant and occurs already at room temperature, almost equimolar amounts of both coupling partners may be used.…”

“…Importantly, as this reaction does not require an addition of an external oxidant and occurs already at room temperature, almost equimolar amounts of both coupling partners may be used. Besides, the [Cp*IrCl 2 ] 2 catalyst may also be used to perform this Sonogashira-type coupling [130]. Noteworthy, a complementary reactivity was observed when using the iridium congener; N-methoxybenzamides failed to undergo the desired alkynylation in the presence of [Cp*RhCl 2 ] 2 catalyst, but the desired reactivity could be restored under the iridium-catalyzed conditions.…”