Unveiling the impact of the light source and steric factors on [2 + 2] heterocycloaddition reactions

Mateos, Javier; Rigodanza, Francesco; Costa, Paolo; Natali, Mirco; Vega‐Peñaloza, Alberto; Fresch, Elisa; Collini, Elisabetta; Bonchio, Marcella; Sartorel, Andrea; Dell’Amico, Luca

doi:10.1038/s44160-022-00191-5

Cited by 25 publications

(13 citation statements)

References 50 publications

(57 reference statements)

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“…One possible pitfall in this strategy is reverse TTET from the photoreactive triplet-excited state of the benzaldehyde ( 3* ArCHO in Figure ) to the annihilator (to form 3* PPO ) or the sensitizer (to result in 3* Ir Naph ). Using an excess of furan (Figure c), it has been possible to counteract this energy-wasting reaction pathway, such that a bimolecular C–C bond forming reaction has become possible, whereas previous related studies dealt mostly with simpler photo-isomerization or photo–fragmentation reactions. , Paternò–Büchi and related cycloaddition reactions are regaining interest in current research, − and our proof-of-concept [2 + 2] cycloadditions shown in Figure c demonstrate that blue-to-UV upconversion can enable these reactions with visible light. Metal–organic bichromophores as sensitizers are useful for this purpose.…”

Section: Resultsmentioning

confidence: 99%

Metal–Organic Bichromophore Lowers the Upconversion Excitation Power Threshold and Promotes UV Photoreactions

Wang

Glaser

et al. 2023

J. Am. Chem. Soc.

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Sensitized triplet−triplet annihilation upconversion is a promising strategy to use visible light for chemical reactions requiring the energy input of UV photons. This strategy avoids unsafe ultraviolet light sources and can mitigate photo-damage and provide access to reactions, for which filter effects hamper direct UV excitation. Here, we report a new approach to make blue-to-UV upconversion more amenable to photochemical applications. The tethering of a naphthalene unit to a cyclometalated iridium(III) complex yields a bichromophore with a high triplet energy (2.68 eV) and a naphthalenebased triplet reservoir featuring a lifetime of 72.1 μs, roughly a factor of 20 longer than the photoactive excited state of the parent iridium(III) complex. In combination with three different annihilators, consistently lower thresholds for the blue-to-UV upconversion to crossover from a quadratic into a linear excitation power dependence regime were observed with the bichromophore compared to the parent iridium(III) complex. The upconversion system composed of the bichromophore and the 2,5-diphenyloxazole annihilator is sufficiently robust under long-term blue irradiation to continuously provide a high-energy singlet-excited state that can drive chemical reactions normally requiring UV light. Both photoredox and energy transfer catalyses were feasible using this concept, including the reductive N−O bond cleavage of Weinreb amides, a C−C coupling reaction based on reductive aryl debromination, and two Paterno−Buchi [2 + 2] cycloaddition reactions. Our work seems relevant in the context of developing new strategies for driving energetically demanding photochemistry with low-energy input light.

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Section: Resultsmentioning

confidence: 99%

Metal–Organic Bichromophore Lowers the Upconversion Excitation Power Threshold and Promotes UV Photoreactions

Wang

Glaser

et al. 2023

J. Am. Chem. Soc.

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“…[54] In this regard, our group have recently showed that the visible light driven cycloaddition of biorelevant indole derivatives 75 with prochiral diketo compounds 76 enables the preparation of complex tridimensional structures such as the endo-and exo-cycloadduct 77 (Scheme 15). [55] Importantly, a thorough mechanistic investigation conducted by DFT calculations, UV/Vis, emission, and transient absorption spectroscopy (TAS) demonstrated that the reaction can proceed through two distinct pathways, namely via exciplex or EDA complex formation and that these two key intermediates lead to the product 77 in opposite diasteroisomeric form. This discovery enabled to channel the reaction towards the formation of either the endo-or the exo-cycloadduct 77 by a judicious selection of the reaction parameters, such as the light source and the steric hinderance of the diketo compound 76.…”

Section: [2+2]-heterocycloadditions Via Direct Irradiation Of An Eda ...mentioning

confidence: 99%

Mechanisms and Synthetic Strategies in Visible Light‐Driven [2+2]‐Heterocycloadditions

et al. 2023

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The synthesis of four membered heterocycles usually requires multi-step procedures and prefunctionalized reactants. A straightforward alternative is the photochemical [2+2]-heterocycloaddition between an alkene and a carbonyl derivative, conventionally based on the photoexcitation of this latter. However, this approach is limited by the absorption profile of the carbonyl, requiring in most of the cases the use of high-energy UV-light, that often results in undesired side reactions and/or the degradation of the reaction components. The development of new and milder visible light-driven [2+2]-heterocycloadditions is, therefore, highly desirable. In this Review, we highlight the most relevant achievements in the development of [2+2]-heterocycloadditions promoted by visible light, with a particular emphasis on the involved reaction mechanisms. The open challenges will also be discussed, suggesting new possible evolutions, and stimulating new methodological developments in the field. Mechanisms for Visible Light [2+2]-Hetero-CycloadditionsA prerequisite for visible light [2+2]-heterocycloadditions is the presence of a photoactive species able to absorb light

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“…Thus, it is clear that the altered diastereomeric ratio seen at shorter wavelengths is associated with the presence of the photosensitiser 9 . Recent reports of the impact of photosensitisers on stereochemical outcome are relevant to this work, 63,64 although in this instance the altered diastereomeric ratio is principally due to selective degradation.…”

Section: Resultsmentioning

confidence: 99%

Flow photolysis of aryldiazoacetates leading to dihydrobenzofurans via intramolecular C–H insertion

et al. 2023

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Unveiling the impact of the light source and steric factors on [2 + 2] heterocycloaddition reactions

Cited by 25 publications

References 50 publications

Metal–Organic Bichromophore Lowers the Upconversion Excitation Power Threshold and Promotes UV Photoreactions

Metal–Organic Bichromophore Lowers the Upconversion Excitation Power Threshold and Promotes UV Photoreactions

Mechanisms and Synthetic Strategies in Visible Light‐Driven [2+2]‐Heterocycloadditions

Flow photolysis of aryldiazoacetates leading to dihydrobenzofurans via intramolecular C–H insertion

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