Rhodium‐Catalyzed CH Alkynylation of Arenes at Room Temperature

Abstract

The rhodium(III)-catalyzed ortho C-H alkynylation of non-electronically activated arenes is disclosed. This process features a straightforward and highly effective protocol for the synthesis of functionalized alkynes and represents the first example of merging a hypervalent iodine reagent with rhodium(III) catalysis. Notably, this reaction proceeds at room temperature, tolerates a variety of functional groups, and more importantly, exhibits high selectivity for monoalkynylation.

Cyclic Hypervalent Iodine Reagents for Atom‐Transfer Reactions: Beyond Trifluoromethylation

“…In 2014, a breakthrough in the alkynylation of SP 2 C-H bonds using transition metal catalysts and EBX reagents was reported independently by three laboratories based on a directing group strategy. [61] Loh and Feng first reported the alkynylation of pivaloyl benzamides using a rhodium(III) catalyst and TIPS-EBX (5) (Scheme 27, A).…”

Alkynylation with Hypervalent Iodine Reagents

“…In 2014, the groups of Li, Loh and Glorius reported nearly simultaneously a directing group strategy for the alkynylation of arenes using rhodium catalysis (Scheme 2.22). The work of Loh and Fang used a pivaloyl benzamide protecting group together with a rhodium(III)-Cp* catalyst and TIPS-EBX 52 as reagent (Scheme 2.22, A [128]). A major advantage in comparison to previously reported C-H alkynylation methods is that the reaction could be performed at room temperature giving excellent yields of products and tolerating many functional groups.…”

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.…”

“…Subsequent reductive elimination would lead to the formation of a Rh(III) alkyne benzoate species, which, after migratory insertion of the benzoate, would give an isolable Rh(III) vinyl complex [130]. Alternatively, a mechanistic scenario involving a regioselective carborhodation by the metallacyclic intermediate, followed by α-elimination affording a rhodium vinylidene complex, intramolecular 1,2-aryl migration, and heterolytic C-Rh bond cleavage (pathway b), can be considered [127]. In addition, a pathway involving the addition of the rhodacycle to an alkyne with concomitant expulsion of 2-iodobenzoic acid affording carbene species was also proposed (pathway c) [129].…”