118,202 research outputs found
Photocatalyzed site- and stereoselective functionalization of β-fucosides
No full textThe modification of carbohydrates plays a crucial role in drug design and development. However, while functionalization at the anomeric position is widely explored, C-H bond activation still remains underdeveloped. In this context, photocatalysis allows access to traditionally hindered reactivity[1] and hydrogen atom transfer (HAT) reactions pave the way towards the direct editing of the sugar backbone.[2]
Here we present the photocatalyzed C-5 functionalization of β-fucosides. This is achieved using decatungstate anion (TBADT) as catalyst: the oxygen centers in its excited state are highly electrophilic[3] and, after deactivation of fucosides’ positions 1-4, they are able to generate an oxygen-stabilized tertiary nucleophilic radical in position 5.
A scope of several fucosides was carried out, with different yields according to the nature of the substituent at the anomeric position. The most promising substrates were treated with several vinylic olefins, achieving full regio- and stereoselectivity.
To the best of our knowledge, this work represents the first example of direct C-H functionalization at position 5 of monosaccharides.
References
1. D.J. Gorelik, S.P. Desai, S. Jdanova, J.A. Turner, M.S. Taylor, Chem Sci 2024, 15, 1204.
2. L. Capaldo, D. Ravelli, M. Fagnoni, Chem. Rev. 2022, 122, 1875.
3. V. De Waele, O. Poizat, M. Fagnoni, A. Bagno, D. Ravelli, ACS Catal. 2016, 6, 7174
Laser Polishing of Polymer Parts Produced with Material Jetting Technology: Effect of Laser Scan Speed, Overlapping and Loop Cycles
No full textIn the last year, the industrial production is characterized by the request of high level of product variety that generates a decrease of production volume changing manufacturing from mass production to mass customization. This trend let the conventional production processes, as forming, casting or moulding, expensive because of initial tools production cost that is not more amortized by the high-volume production. A solution to this scenario is to integrate Additive Manufacturing in tools production; this solution guarantees tools cost reduction also if post processes operations are needful to reduce the surface roughness produced by additive processes. Among additive processes, Material Jetting is able produce parts with guaranteed high accuracy and low average surface roughness (0.5 μm). However, these standards mainly refer to upfacing surfaces parallel to the print plate, and the roughness obtained on the other surfaces could increase up to 15 μm because of production mechanism. To improve parts roughness in this study, the laser polishing process was tested; different experimental tests were executed to investigate the effects of scan speed, overlapping and loop cycles. The results demonstrated that it is possible to improve the surface finish and reduce the roughness by 70% at the expense of dimensional accuracy
Decatungstate as Direct Hydrogen Atom Transfer Photocatalyst for SOMOphilic Alkynylation
No full textA versatile approach for the alkynylation of a variety of aliphatic hydrogen donors, including alkanes, is reported. We used tetrabutylammonium decatungstate as photocatalyst to generate organoradicals from C–H/Si–H bonds via hydrogen atom transfer. The latter intermediates underwent SOMOphilic alkynylation by methanesulfonyl alkynes to afford internal alkynes upon loss of a sulfonyl radical. The effect of different radicofugal groups on the reaction outcome was evaluated and rationalized via a combined experimental and computational approach
The Dark Side of Photocatalysis: One Thousand Ways to Close the Cycle
No full textPhotocatalytic strategies have recently revolutionized the field of organic synthesis. However, while the progress has been impressive in terms of reported methodologies, less attention has been devoted to mechanistic aspects. In this regard, key to the development of efficient strategies is the recovery of the exhausted photocatalyst formed upon quenching of the excited state. This review summarizes the different ways available to turn over the photocatalyst and classifies them according to the species responsible for this step, being a reaction intermediate, a co-catalyst, a reaction partner or an electrode. Finally, an analysis of the common aspects of the described alternatives is offered, also showcasing how the tuning of the photocatalyst turn-over step can completely divert the reaction outcome
Photocatalytic hydrogen atom transfer: the philosopher's stone for late-stage functionalization?
No full textAn overview about the potentialities of photocatalytic Hydrogen Atom Transfer (HAT) for the Late-Stage Functionalization (LSF) of complex molecules is offered. The examined approach allows the smooth homolytic cleavage of the C-H bonds embedded in the substrate, offering a straightforward access to valuabe C-centred radical intermediates to be exploited for the desired transformations. The examples have been classified according to the species responsible for the activation of the substrate, also showcasing the opportunities in terms of selectivity offered by the different alternatives
Età pensionabile nel pubblico impiego e discriminazioni di sesso secondo la Corte di giustizia (C-46/07)
No full textCessione di ramo d'azienda nelle imprese in crisi e applicazione dei principi di razionalità e buona fede
No full textControlli informatici e tutela della privacy: alla ricerca di un difficile punto di equilibrio
No full textPolymer Shaped Punches Produces with Fused Filament Fabrication to Improve Cup Accuracy in Sheet Metal Forming
No full textRapid tooling has become an effective solution for reducing time and costs in tool production. In sheet metal forming, polymer tools produced via additive manufacturing offer performance comparable to traditional tools. However, a key challenge in this area is compensating for the radial expansion of polymer tools during the forming process, which leads to reduced accuracy in the produced parts and limits the achievable forming depth. To address this issue, the authors of this study proposed a novel punch design aimed at containing radial expansion, thereby enabling greater drawing depth and improved part accuracy. Different punch geometries were designed with a re-entrant angle varying between 150° and 180°. Numerical simulations were conducted to evaluate the optimal geometry, identifying the 160° angle as the best option to compensate for radial expansion and reduce punch load. Experimental tests were then performed to verify the numerical results, demonstrating the potential of this new design producing cups with higher drawing depth and best radial accuracy
- …
