Arene Activation through Iminium Ions: Product Diversity from Intramolecular Photocycloaddition Reactions.

While 2-alk-ω-enyloxy-sustituted benzaldehydes do not display any photochemical reactivity at the arene core, the respective iminium perchlorates were found to undergo efficient reactions either upon direct irradiation (λ=366 nm) or under sensitizing conditions (λ=420 nm, 2.5 mol% thioxanthen-9-one). Three pathways were found: (a) Most commonly, the reaction led to benzoxacyclic products in which the olefin in the tether underwent a formal, yet unprecedented carboformylation (13 examples, 44-99 % yield). The cascade process occurred with high diastereoselectivity and was found to be stereoconvergent. (b) If a substituent resides in the 3-position of the benzene ring, a meta photocycloaddition was observed which produced tetracyclic skeletons with five stereogenic centers in excellent regio- and diastereoselectivity (2 examples, 58-79 % yield). (c) If the tether was internally substituted at the alkene, an arene photocycloaddition was avoided and an azetidine was formed in an aza Paternò-Büchi reaction (2 examples, 95-98 % yield). © 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.

Citation

Johanna Proessdorf, Christian Jandl, Thomas Pickl, Thorsten Bach. Arene Activation through Iminium Ions: Product Diversity from Intramolecular Photocycloaddition Reactions. Angewandte Chemie (International ed. in English). 2022 Sep 02;61(40):e202208329

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PMID: 35920713

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