Bisoxazoline-functionalised enantioselective monolithic mini-flow-reactors: development of efficient processes from batch to flow conditions

Burguete, M. Isabel; Cornejo, Alfonso; García‐Verdugo, Eduardo; García, Juan Rafael; Gil, María José; Luis, Santiago V.; Martínez‐Merino, Víctor; Mayoral, José A.; Sokolova, Maia

doi:10.1039/b704465h

Cited by 55 publications

(41 citation statements)

References 44 publications

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“…[1,72] A number of groups have published research making or using a-diazocarbonyl reagents in flow. [73][74][75][76][77][78][79][80][81] Ethyl diazoacetate (17) is one of the few commercially available diazo compounds and a useful C2 synthon. [1] It is therefore no surprise that the first examples of a-diazocarbonyl chemistry in continuous processing make use of this reagent.…”

Section: Other Diazoalkanesmentioning

confidence: 99%

Taming Hazardous Chemistry in Flow: The Continuous Processing of Diazo and Diazonium Compounds

Deadman

Collins

Maguire

2014

Chemistry A European J

178

104

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Type of publicationArticle ( 1 This is the pre-peer reviewed version of the following article: Deadman, B. J., Benjamin J. Deadman, [a] Stuart G. Collins [a] and Anita R. Maguire* [b] 2 This is the pre-peer reviewed version of the following article: Deadman, B. J., , Taming Hazardous Chemistry in Flow: The Continuous Processing of Diazo and Diazonium Compounds. Chem. Eur. J. which has been published in final form at http://dx.doi.org/10.1002/chem.201404348 DOI: 10.1002/chem.201404348 IntroductionDiazo and diazonium compounds are extremely versatile intermediates and reagents in organic synthesis. Diazoalkanes are important alkylating reagents, [1,2] while α-diazocarbonyls are important for their role in generating carbenes and metal carbenoids, [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and also for providing access to reactive ketene and heteroanalogous intermediates via the Wolff rearrangement. [21][22][23][24][25][26] Diazo compounds are also important 1,3-dipoles for heterocycle-forming cycloaddition reactions. [27][28][29][30][31][32] The diazonium ion moiety is an important leaving group in Sandmeyer, [33][34][35] Meerwein, [36,37] Balz-Schiemann [38,39] and palladium catalysed cross coupling [40][41][42] chemistry; and is an essential reagent for the preparation of azo compounds, the backbone of the synthetic dye industry. [42,43] The versatility of the diazo and diazonium moieties is matched only by their fearsome reputation. Diazoalkanes are highly toxic due to their potent alkylation of DNA. [44] Furthermore, diazo and diazonium compounds are highly energetic by nature and explosions can be triggered by shock, heat or exposure to concentrated acids. [44,45] α-Diazocarbonyls are considerably more stable than diazoalkanes and diazoniums due to the resonance stabilisation of adjacent carbonyls but detonation is still possible under more forcing conditions. [44,46] These safety concerns necessitate caution when using diazo and diazonium intermediates in the laboratory, and have limited their use on scale in industry. The synthetic utility of these hazardous compounds has led to a recent interest in developing safer alternative methods for their preparation and use. [1,44] Continuous processing is rapidly growing in the academic, pharmaceutical and fine chemical sectors due to its favourable safety profile among other benefits such as efficient mixing, enhanced heat and mass transfer, access to extreme reaction conditions, reproducibility and scale up, in-line workups and automated operation. [47][48][49][50][51][52][53][54] The safety profile offered by continuous processing is perhaps the most compelling reason for its popularity in recent years. Sensitive and toxic reaction intermediates can be generated and consumed during a single flow process without the need for stockpiling hazardous quantities of material. Furthermore, the high surface area-tovolume ratio of tubular flow reactors also ensures rapid dissipation of heat and reduces the risk of reaction runaway.Continuou...

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Section: Other Diazoalkanesmentioning

confidence: 99%

Taming Hazardous Chemistry in Flow: The Continuous Processing of Diazo and Diazonium Compounds

Deadman

Collins

Maguire

2014

Chemistry A European J

178

104

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“…The cyclopropanation of styrene using ethyl diazo acetate was selected as the benchmark process ( Figure 5.16). The results gathered in this study revealed that all those parameters are of great importance for the final outcome and that important differences can be found when those results are compared with those of related batch processes [44]. Thus, the flow rate was a critical parameter to be controled in terms of conversion and selectivity.…”

Section: Enantioslective Cyclopropanation Reactionsmentioning

confidence: 83%

Continuous Flow System Using Polymer‐Supported Chiral Catalysts

Luis

García‐Verdugo

2011

Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis

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“…The preparation of this kind of catalyst in the form of monolithic polymers inside stainless steel columns is very well suited to work under flow conditions [76–77]. Both catalysts were studied in flow conditions with scCO 2 (40 °C, 8 MPa), with conventional solvents and under solvent-free conditions [74,78–79]. One of the main outcomes of the results obtained was the observation of a significant improvement in the productivity when going from conventional to supercritical conditions within the same reactor.…”

Section: Reviewmentioning

confidence: 99%

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids

Burguete¹,

García‐Verdugo²,

Luis³

2011

Beilstein J. Org. Chem.

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SummaryThis paper reviews the current trends in the combined use of supported catalytic systems, either on solid supports or in liquid phases and supercritical fluids (scFs), to develop selective and enantioselective chemical transformations under continuous and semi-continuous flow conditions. The results presented have been selected to highlight how the combined use of those two elements can contribute to: (i) Significant improvements in productivity as a result of the enhanced diffusion of substrates and reagents through the interfaces favored by the scF phase; (ii) the long term stability of the catalytic systems, which also contributes to the improvement of the final productivity, as the use of an appropriate immobilization strategy facilitates catalyst isolation and reuse; (iii) the development of highly efficient selective or, when applicable, enantioselective chemical transformations. Although the examples reported in the literature and considered in this review are currently confined to a limited number of fields, a significant development in this area can be envisaged for the near future due to the clear advantages of these systems over the conventional ones.

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Bisoxazoline-functionalised enantioselective monolithic mini-flow-reactors: development of efficient processes from batch to flow conditions

Abstract: Monolithic polymers functionalised with BOX-Cu moieties can be applied for the cyclopropanation reaction under batch and flow conditions using either conventional or supercritical solvents.

Cited by 55 publications

References 44 publications

Taming Hazardous Chemistry in Flow: The Continuous Processing of Diazo and Diazonium Compounds

Taming Hazardous Chemistry in Flow: The Continuous Processing of Diazo and Diazonium Compounds

Continuous Flow System Using Polymer‐Supported Chiral Catalysts

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids

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