Radical Cation Cyclopropanations via Chromium Photooxidative Catalysis

Sarabia, Francisco; Ferreira, Eric M.

doi:10.1021/acs.orglett.7b01095

Cited by 46 publications

(35 citation statements)

References 42 publications

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“…[6] Despite this deficiency, applications of molecular chromium(III) complexes,s uch as [Cr(phen) 3 ] 3+ derivatives,i no xidative photoredox catalysis have been recently developed capitalizing on the high excited state redox potential (phen = 1,10-phenanthroline). [8][9][10][11] In contrast to previously reported molecular Cr 3+ complexes is the recently reported intense solution luminescence of [Cr-(ddpd) 2 ] 3+ (Scheme 1, ddpd = N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine). This complex can be considered am olecular ruby analogue due to its exceptionally high quantum yields of 10-14 %i ns olution at room temperature and up to 30 %f or deuterated derivatives.…”

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confidence: 82%

Molecular Ruby under Pressure

et al. 2018

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The intensely luminescent chromium(III) complexes [Cr(ddpd) ] and [Cr(H tpda) ] show surprising pressure-induced red shifts of up to -15 cm kbar for their sharp spin-flip emission bands (ddpd=N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine; H tpda=2,6-bis(2-pyridylamino)pyridine). These shifts surpass that of the established standard, ruby Al O :Cr , by a factor of 20. Beyond the common application in the crystalline state, the very high quantum yield of [Cr(ddpd) ] enables optical pressure sensing in aqueous and methanolic solution. These unique features of the molecular rubies [Cr(ddpd) ] and [Cr(H tpda) ] pave the way for highly sensitive optical pressure determination and unprecedented molecule-based pressure sensing with a single type of emitter.

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confidence: 82%

Molecular Ruby under Pressure

et al. 2018

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“…Based on previous studies on the reaction of diazoacetate derivatives with alkene cation radicals, we initially hypothesized that following nucleophilic addition to the aromatic cation radical, electron transfer from the reduced form of the catalyst to the generated cyclohexadienyl radical could trigger a 1,2‐hydride shift and expulsion of N 2 , leading to the formation of the observed C−H functionalization product ( IV , Figure ). Such a mechanism would be reminiscent of that proposed for the cyclopropanation of alkene cation radicals by Ferreira and Sarabia . When utilizing d 3 ‐mesitylene as a substrate, no deuterium incorporation was observed in the C−H alkylation product, suggesting that a 1,2‐hydride shift is an unlikely step in the mechanism ( II , Figure ).…”

Section: Methodsmentioning

confidence: 76%

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

2020

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Expanding the toolbox of C−H functionalization reactions applicable to the late‐stage modification of complex molecules is of interest in medicinal chemistry, wherein the preparation of structural variants of known pharmacophores is a key strategy for drug development. One manifold for the functionalization of aromatic molecules utilizes diazo compounds and a transition‐metal catalyst to generate a metallocarbene species, which is capable of direct insertion into an aromatic C−H bond. However, these high‐energy intermediates can often require directing groups or a large excess of substrate to achieve efficient and selective reactivity. Herein, we report that arene cation radicals generated by organic photoredox catalysis engage in formal C−H functionalization reactions with diazoacetate derivatives, furnishing sp2–sp3 coupled products with moderate‐to‐good regioselectivity. In contrast to previous methods utilizing metallocarbene intermediates, this transformation does not proceed via a carbene intermediate, nor does it require the presence of a transition‐metal catalyst.

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“…Such a mechanism would be reminiscent of that proposed for the cyclopropanation of alkene cation radicals by Ferreira and Sarabia. [22] When utilizing d 3 -mesitylene as a substrate, no deuterium incorporation was observed in the C À H alkylation product, suggesting that a 1,2-hydride shift is an unlikely step in the mechanism (II, Figure 2). When d 1 -TFE is used as the reaction solvent, a mixture of non-deuterated, mono-deuterated, and di-deuterated products is observed with the monodeuterated formed as the major product in 72 % yield.…”

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confidence: 99%

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

2020

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Expanding the toolbox of C À H functionalization reactions applicable to the late-stage modification of complex molecules is of interest in medicinal chemistry, wherein the preparation of structural variants of known pharmacophores is a key strategy for drug development. One manifold for the functionalization of aromatic molecules utilizes diazo compounds and a transition-metal catalyst to generate a metallocarbene species, which is capable of direct insertion into an aromatic CÀH bond. However, these high-energy intermediates can often require directing groups or a large excess of substrate to achieve efficient and selective reactivity. Herein, we report that arene cation radicals generated by organic photoredox catalysis engage in formal C À H functionalization reactions with diazoacetate derivatives, furnishing sp 2 -sp 3 coupled products with moderate-to-good regioselectivity. In contrast to previous methods utilizing metallocarbene intermediates, this transformation does not proceed via a carbene intermediate, nor does it require the presence of a transitionmetal catalyst.Metallocarbenes are reactive organometallic species that may be generated by using a transition-metal precursor and diazoacetate derivatives. [1][2][3] The resulting carbene intermediate may then undergo CÀH insertion with reactive CÀH bonds (often aryl or alkyl), affording the corresponding alkylated adducts. However, owing to the high reactivity of metallocarbenes, aromatic substrates are often required to be present in excess for efficient reactivity.Among methodologies based on metallocarbene CÀH insertion that do not use a several-fold excess of arene, directing groups are often required. The groups of Fox [4] and Wang [5] have reported ortho-selective C À H functionalization of heterocycles by using diazoacetates. In addition, other directing groups, such as purines, [6] azacycles, [7] disubstituted anilines, [8] and phenols, [9] have been utilized in metallocarbene CÀH alkylation reactions. Collectively, these directing groups limit the synthetic applicability of metallocarbene C À H alkylation reactions.Recently, Suero and co-workers reported the synthesis of aryl diazoacetate derivatives under photoredox conditions. [10]

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Radical Cation Cyclopropanations via Chromium Photooxidative Catalysis

Cited by 46 publications

References 42 publications

Molecular Ruby under Pressure

Molecular Ruby under Pressure

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

Regioselective Arene C−H Alkylation Enabled by Organic Photoredox Catalysis

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