Rhodium-Catalyzed Alkenylation of Arenes with Multi-Substituted Olefins: Comparison of Selectivity and Reaction Rate as a Function of Olefin Identity

Abstract

Rhodium-catalyzed arene alkenylation using Cu(II) carboxylates as the in situ oxidant and mono-substituted olefins has been previously reported (e.g., J. Am. Chem. Soc. 2019, 139, 5474; J. Am. Chem. Soc. 2018, 140, 17007; Organometallics 2019, 38, 3860; J. Am. Chem. Soc. 2020, 142, 10534). Herein, studies are extended to multi-substituted olefins with the goal of evaluating the effect of olefin substitution pattern and substituent identity on selectivity and turnover frequency. The influence of olefin substitution is probed by comparing the conversion of benzene to alkenyl arenes with ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, isobutene, 2-methyl-2-butene, and tetramethylethylene as well as the phenyl-substituted olefins and isomers of propenylbenzene. The rate of oxidative hydrophenylation for multi-substituted olefins follows the trend monosubstituted > disubstituted > trisubstituted, and tetrasubstituted olefins are unreactive. To probe the effect of substituent size on Markovnikov/anti-Markovnikov regioselectivity, cyclohexyl, tert-butyl, isopropyl, ethyl, and methyl substituted α-olefins are compared. Selectivity for anti-Markovnikov products generally increases as substituent steric bulk is increased. Tolerance for some functionalized olefins is demonstrated. The ortho/meta/para regioselectivity with mono-substituted arenes reveals that arene and olefin identity influences selectivity. Further mechanistic studies provide evidence for Curtin–Hammet control of ortho/meta/para regioselectivity with monosubstituted arenes.

Highly Anti-Markovnikov Selective Oxidative Arene Alkenylation Using Ir(I) Catalyst Precursors and Cu(II) Carboxylates

“…In addition to catalytic arene alkylation using arenes and olefins, Ru, , Rh, ,,− and Pd − catalysts for single-step oxidative arene alkenylation have been reported. The general mechanisms reported for arene alkenylation using Rh and Pd include arene C–H activation, olefin insertion into a M–aryl bond, and product-forming β-H elimination, which is followed by the dissociation of alkenyl arenes.…”

“…For arene alkenylation using α-olefins, the Rh­(I) dimer [Rh­(μ-OAc)­(C 2 H 4 ) 2 ] 2 and (5-FP)­Rh­(TFA)­(C 2 H 4 ) (5-FP = 1,2-bis­( N -7-azaindolyl)-benzene; TFA = trifluoroacetate) are selective for the linear products over the branched products (Scheme ). , The selectivity changes as a function of reaction conditions such as temperature, oxidant identity, and oxidant concentration with observed linear/branched (L/B) ratios between 6:1 and 18:1. , Also, we studied arene alkenylation with multisubstituted olefins using [Rh­(μ-OAc)­(C 2 H 4 ) 2 ] 2 as a catalyst precursor and Cu­(II) carboxylate salts as the in situ oxidant . The selectivity for anti-Markovnikov products generally increases with steric bulk of the olefin, with vinyl cyclohexane giving a 27(1):1 anti-Markovnikov/Markovnikov product ratio and 1-butene giving a 7.7(6):1 anti-Markovnikov/Markovnikov product ratio.…”

“… 15 , 16 Also, we studied arene alkenylation with multisubstituted olefins using [Rh(μ-OAc)(C 2 H 4 ) 2 ] 2 as a catalyst precursor and Cu(II) carboxylate salts as the in situ oxidant. 49 The selectivity for anti-Markovnikov products generally increases with steric bulk of the olefin, with vinyl cyclohexane giving a 27(1):1 anti-Markovnikov/Markovnikov product ratio and 1-butene giving a 7.7(6):1 anti-Markovnikov/Markovnikov product ratio. Additionally, monosubstituted olefins react faster than disubstituted olefins, and trisubstituted olefins are minimally reactive.…”

Rhodium-Catalyzed Oxidative Alkenylation of Anisole: Control of Regioselectivity

“…51 The use of Cu(II) carboxylates as in situ oxidants allows overall aerobic oxidation since the reduced Cu(I) can be oxidized using dioxygen or unpurified air to regenerate Cu(II) (Scheme 2). 15,41,[44][45][46]48,50,53,54 Based on our previous studies of oxidative arene alkenylation using [(η 2 -C 2 H 4 ) 2 Rh(μ-OAc)] 2 as a catalyst precursor, we envisioned a process for which anisole and propylene in the presence of the same Rh catalyst precursor and CuX 2 (X = acetate, pivalate, and 2-ethylhexanoate) oxidant would yield propenylanisoles. Although we have previously reported the alkenylation of substituted arenes (e.g., toluene, trifluorotoluene, and anisole) using [(η 2 -C 2 H 4 ) 2 Rh(μ-OAc)] 2 and Pd-(OAc) 2 precursors and CuX 2 as an in situ oxidant, we have not completed a study specifically using anisole and ethylene or propylene.…”

Ferrocene catalyzed carbohydroxylation of alkenes using H2O and cycloketone oxime esters

“…The continuous exploration of novel, environmentally friendly methods for the functionalization of readily available olefins remains a prominent area of research in the field of synthetic organic chemistry. Despite the availability of several catalytic approaches for the mono- and difunctionalization of alkenes using transition metals such as nickel, 1 palladium, 2 copper, 3 gold, 4 rhodium, 5 and iron, 6 as catalysts, there is still significant interest in expanding the range of methodologies. Furthermore, the utilization of photoredox and photochemical strategies has also emerged as a promising avenue for achieving olefin functionalization.…”