Direct Prenylation of Aromatic and α,β-Unsaturated Carboxamides via Iridium-Catalyzed C−H Oxidative Addition−Allene Insertion

Abstract

Exposure of aromatic carboxamides 1e-1m, heteroaromatic carboxamides 1n-1p, and r,β-unsaturated carboxamides 1q-1s to 1,1dimethylallene in the presence of the a cationic iridium complex derived from [Ir(cod) 2 ]BAr F 4 and rac-BINAP results in direct C-H prenylation to furnish adducts 2e-2m, 2n-2p, and 2q-2s, respectively, in good isolated yields as single isomers.Enzymatic prenyl transfers are heavily trafficked biosynthetic pathways, 1 yet synthetic catalysts for C-H prenylation are unknown. [2][3][4] Having recently developed protocols for catalytic carbonyl prenylation employing 1,1-dimethylallene as the prenyl donor, 5 catalytic ortho-C-H insertion of 1,1dimethylallene was viewed as a potential strategy for the direct prenylation of aryl C-H bonds. Due largely to the pioneering efforts of Murai, 6 Lewis base-directed catalytic C-H activation initiated olefin insertions, and alkyne inser-

Development of Novel and Highly Efficient Methods to Construct Carbon–Carbon Bonds Using Group 7 Transition-Metal Catalysts

“…During our investigations, one example of iridium-catalyzed insertion of an allene into an aromatic CH bond was reported, however the reaction point is quite different from our reaction. 34 The reaction occurs at the terminal position (¡-position) of an allene, whereas our reaction proceeds at the ¢-position of the allene. In addition, another group reported a similar reaction by using a rhodium catalyst at almost the same time of our report.…”

Rhodium-catalyzed mild and selective C–H allylation of indolines and indoles with 4-vinyl-1,3-dioxolan-2-one: facile access to indolic scaffolds with an allylic alcohol moiety

“…7a,c In addition, Krische reported the Ir(I)-catalyzed allylation of benzamides using allenes as allyl sources. 8 Alternatively, our group demonstrated the Ru(II)-catalyzed terminal allylation of (hetero) aromatic and a,b-unsaturated carboxamides with allylic carbonates. 9b Recently, Li described the beautiful studies on the Rh(III)-catalyzed CeH functionalization of arenes with strained N-Ts aziridines and vinyl oxiranes, leading to the formation of b-branched amines 15 and allylic alcohols.…”

High-Valent Co(III)- and Ni(II)-Catalyzed C–H Activation

“…The vast majority of reports of iron, cobalt, and nickel catalyzed C-H activation reactions use low-valent species that are proposed to activate C-H bonds via oxidative addition [26]. Mechanistically, this is analogous to lowvalent Rh(I), Ru(0), and Ir(I) C-H activation reactions that also occur via oxidative addition [27][28][29][30]. Many early reports of first-row metal catalyzed C-H activation took advantage of the mechanistic similarity by reproducing reactions catalyzed by precious metals.…”