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Densely-Functionalized Bicyclic Cyclopentanones by Combined Photoinduced 6-endo-trig Giese Additions and Mild Aldol Cyclizations

Published inOrganic chemistry frontiers, vol. 13, p. 3021-3029
Publication date2026-01-26
First online date2026
Abstract

Polycyclic scaffolds are central to numerous natural products and pharmaceuticals, motivating concise, stereocontrolled routes to their construction. We report a photoredox-enabled synthesis of trans-fused [n.3.0] bicyclic ketones (n = 4, 5, 10) from malonate-derived enol ethers. α-Brominated intermediates, formed by acylation with 2-bromo-2-methylpropanoyl bromide, undergo radical cyclization under two complementary conditions: (i) acridinium orange (AOH+) with Hantzsch ester (HE) at 455 nm, or (ii) photoexcited HE alone at 365 nm. Both modes trigger 6-endo-trig Giese addition, C–O bond fragmentation, and hydrogen-atom transfer to α-branched cyclic ketones that ring-close under mild Brønsted or Lewis acid activation to trans-fused products with exclusive junction control. Mechanistic studies (Stern–Volmer, UV–Vis, electrochemistry) support two activation pathways — AOH+* quenching by HE or direct HE excitation — each generating the same radical intermediates in fine. DFT calculations validate mechanistic pathways and regioselectivity in favor of a philicity matching of the electrophilic radical and the polar electron-rich enol ether. The method accommodates ring-size diversity, accesses trans-hydrindanone architectures, and outcompetes 5-exo-trig spirocyclization.

Citation (ISO format)
VINAS, Julia et al. Densely-Functionalized Bicyclic Cyclopentanones by Combined Photoinduced 6-endo-trig Giese Additions and Mild Aldol Cyclizations. In: Organic chemistry frontiers, 2026, vol. 13, p. 3021–3029. doi: 10.1039/D5QO01635E
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Journal ISSN2052-4110
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Creation28/01/2026 07:29:44
First validation28/01/2026 12:45:37
Update26/05/2026 09:45:42
Status update26/05/2026 09:45:42
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