Synthese mit perfekter Atomökonomie: Erzeugung von Diazoketonen durch 1,3‐dipolare Cycloaddition von Distickstoffmonoxid an cyclische Alkine unter milden Bedingungen

Banert, Klaus; Plefka, Oliver

doi:10.1002/ange.201101326

Cited by 19 publications

(9 citation statements)

References 72 publications

(26 reference statements)

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“…[15] Its reaction with benzyl azide in CD 3 CN proceeded cleanly with a second-order rate constant of (4.0 ± 0.4)M −1 s −1 , the fastest reported cycloalkyne–azide reaction to date (see Figures S3 and S4 in the Supporting Information). During the preparation of this manuscript, Banert and Plefka reported that TMTH was more reactive than a DIBO-like cyclooctyne in a 1,3-dipolar cycloaddition with nitrous oxide, [16] a result that is consistent with our findings.…”

supporting

confidence: 90%

Thiacycloalkynes for Copper‐Free Click Chemistry

et al. 2012

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supporting

confidence: 90%

Thiacycloalkynes for Copper‐Free Click Chemistry

et al. 2012

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“…The formation of the mixed product could be favored by using a 1:2 ratio of the starting materials, but the final yield of the cross-coupling product was still below 50 %. In line with the low reactivity of tert-butylmagnesium bromide in the homocoupling reactions, the cross-coupling with phenylmagnesium chloride was not very efficient ( Table 4, entry 5), whereas very good selectivities were obtained for oxidative alkenyl-alkyl cross-coupling reactions ( Table 4, entries [6][7][8]. The coupling of phenylmagnesium chloride with phenethylmagnesium chloride gave biphenyl, bibenzyl and diphenylbutane in the molar ratio 11:85:4, which is quite distinct from the statistical distribution of 1:2:1.…”

Section: Methodsmentioning

confidence: 98%

“…Heterogeneous catalysts have been used with good success for the activation of N 2 O, but high temperatures and/or pressures are typically required to achieve acceptable reaction rates. [6] Furthermore, the reported turnover numbers are modest ( 100). Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve.…”

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confidence: 99%

Oxidative Coupling Reactions of Grignard Reagents with Nitrous Oxide

2013

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Nitrous oxide ("laughing gas", N 2 O) is a potent oxidation agent, from a thermodynamic point of view. [1] Moreover, it is an environmentally benign oxidant, because the side product is dinitrogen. An obstacle in using N 2 O in oxidation reactions is the inert nature of the gas. Heterogeneous catalysts have been used with good success for the activation of N 2 O, but high temperatures and/or pressures are typically required to achieve acceptable reaction rates. [2] Thus far, N 2 O-based oxidation reactions with homogeneous catalysts in solution have met with only limited success. Many transition-metal complexes are known to react with N 2 O under mild conditions, [3] but catalytic turnover is difficult to achieve. Some polyoxometalates [4] and ruthenium complexes [5] were shown to catalyze oxidation reactions with N 2 O, but the reactions require high temperatures (100-200 8C) and often elevated pressures. [6] Furthermore, the reported turnover numbers are modest ( 100). Herein, we describe oxidative carbon-carbon coupling reactions with N 2 O, which can be performed under mild conditions with good selectivity and unprecedented turnover numbers.Oxidative homo-and cross-coupling reactions of Grignard reagents [7,8] in the presence of metal catalysts can be achieved with different oxidants, including 1,2-dihaloethanes [9] and dioxygen. [10] The reactions are believed to involve low-valent organometallic complexes. [7][8][9][10] We hypothesized that these low-valent, nucleophilic complexes might be susceptible to oxidation by N 2 O. As a model reaction, we studied the homocoupling of phenylmagnesium chloride. The reactions were performed in THF at room temperature under an atmosphere of N 2 O using different transition-metal salts as potential catalysts (Li 2 CuCl 4 , Li 2 MnCl 4 , CoCl 2 , FeCl 3 , [Fe(acac) 3 ]). To avoid reactions caused by traces of dioxygen, we have used N 2 O of high purity (99.999 %). Test reactions with metal salt (1 mol %) gave the oxidative coupling product biphenyl after 1 h in yields of 30-95 % (Table 1, entries 1-5). The best results were found for FeCl 3 (94 % yield), [Fe(acac) 3 ] (94 % yield) and CoCl 2 (95 % yield). The latter two complexes were used for further studies.First, we examined the efficiency of the reaction. Lowering the amount of catalyst from 1.0 mol % to 0.1 mol % had no effect on the yield. Further reduction to 0.01 mol % gave a poor yield in the case of [Fe(acac) 3 ], even if the reaction time was prolonged. With CoCl 2 , however, the catalyst loading could be reduced to 0.004 mol % and biphenyl was still obtained in 83 % yield (Table 1, entry 7). Taking into account the small amount of product formed without catalyst (8 % after 18 h), and assuming that one catalytic cycle produces one biphenyl molecule, we can calculate a turnover number of 9.4 10 3 . This value greatly exceeds what has been reported thus far for metal-catalyzed oxidation reactions with N 2 O in homogeneous solution. [4,5] The groups of Lei [10c] and Cahiez [10d] have shown that Fe complexes ar...

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“…To avoid this problem, we established a route to cyclooct‐2‐ynol ( 13 ) by starting from cyclooctene ( 9 ; see Scheme ). The first steps comprised a Wohl–Ziegler bromination followed by a sequence of bromination and elimination reactions as described in the literature 17. Next, the hydrolysis of dibromocyclooctene 10 to give the corresponding alcohol 11 was carried out by using a DMSO/water mixture 18.…”

Section: Resultsmentioning

confidence: 99%

“… Reagents and conditions for the cyclooctynol synthesis: (a) N ‐bromosuccinimide (NBS), azobis(isobutyronitrile) (AIBN), CCl 4 , 2 h, reflux, 51 %; then (1) Br 2 , dichloromethane (DCM), –40 °C, 1 h; (2) KO t Bu, tetrahydrofuran (THF), –50 °C, 3 h, 52 %, see Banert et al17; (b) CuSO 4 · 5H 2 O, dimethyl sulfoxide (DMSO), H 2 O, reflux, 2 h, 51 %; (c) Dihydropyran (DHP), Py · TosOH, DCM, 3 h, 99 % (THP = tetrahydropyran); d) (1) LDA, THF, –78 °C to r.t., 12 h; (2) TosOH, MeOH, 2 h, room temp., 36 % over two steps. …”

Section: Resultsmentioning

confidence: 99%