Photoredox catalytic cyclization of aryl enones in the presence of visible light, promoted either by metals or organic dyes, represent a valuable strategy for the synthesis of cycloalkanes. The development of a stereoselective version of such transformation, in the presence of the metal‐free catalyst Eosin Y was studied, with the aim to realize an efficient protocol for the in‐flow synthesis of enantiomerically enriched functionalized cyclopentane rings, taking advantage of the flow reactors technology. The use of a chiral auxiliary on the bisenone to be cyclized offers a straightforward and convenient option to exert a stereocontrol on the light‐driven cyclization. By exploiting Evans’ oxazolidinones, the stereoselective light‐driven cyclization affords, after the removal of the chiral auxiliary, a functionalized 1,2‐trans cyclopentane ring in up to 83/17 enantiomeric ratio. When the reaction was performed in continuo, in a homemade coil photoreactor, high yields were observed. The cyclization was also successfully realized in a 3D‐printed mesoreactor, without any change in the diastereoseletctivity of the process.
A modified pathway towards 5-hydroxy-isoxazolidines has been preliminarily investigated by taking advantage of the anti-Markovnikov route in ene reactions of sterically encumbered nitrosocarbonyl intermediates in the presence of allylsilylethers. Fluoride-mediated deprotection/cyclization of the ene adducts afforded the desired heterocycles in quantitative yields and the methodology is adaptable to a one-pot procedure.[a] Dr. Scheme 3. Synthesis of protected allylic alcohols as silylethers. Scheme 4. Ene reactions of mesito nitrosocarbonyl 8 M with allylsilylethers 16 a-c(A). Yields (%) of the isolated compounds 10, 17 and 18. Mes = 2,4,6-Me 3 Ph.
The Front Cover shows how, like in a modern factory, it is possible to use light to build complex molecules in a continuous process. By exploiting chiral oxazolidinones, an efficient protocol for the in‐flow synthesis of enantiomerically enriched functionalized cyclopentane rings has been developed. The stereoselective light‐driven cyclization of bis(enones) in a coil photoreactor affords enantio‐enriched cyclopentanes. The possibility to perform the cyclization in a 3D‐printed mesoreactor was also successfully demonstrated. The authors acknowledge Dr. Sergio Rossi for the Cover picture idea. More information can be found in the Communication by M. Benaglia et al.
Two new families of N,O‐nucleoside analogues containing the anthracene moiety introduced through the nitrosocarbonyl ene reaction with allylic alcohols were prepared. The core structure is an isoxazolidine heterocycle that introduces either atom either a phenyl ring or dimethyl moiety at the C3 carbon. Different heterobases were inserted at the position 5 of the heterocyclic ring. One of the synthesized compounds demonstrated a good capacity to induce cell death and an appreciable nuclear fragmentation was evidenced in treated cells.
The Cover Feature shows the fluorescence microscopy image inserted in a Petri dish of representative slides showing the effects of active isoxazolidine N,O‐nucleoside treatment on U937 cells. The N,O‐nucleoside was prepared through N‐glycosilation (Vorbrüggen protocol) with 6‐chloropurine of the anti‐Markovnikov ene adduct of the anthracene nitrosocarbonyl intermediate with trans‐cinnamyl alcoho. More information can be found in the Full Paper by Andrea Marraffa et al.
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