Arene Activation through Iminium Ions: Product Diversity from Intramolecular Photocycloaddition Reactions. Issue 40 (2nd September 2022)

• Record Type: Journal Article
• Authors: Proessdorf, Johanna; Jandl, Christian; Pickl, Thomas; Bach, Thorsten
• Is Part Of: Angewandte Chemie international edition. Volume 61:Issue 40(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-02
• Subjects: Cycloaddition -- Oxygen Heterocycles -- Photochemistry -- Rearrangement -- Sensitizers; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202208329
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: 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). Abstract : Benzaldehyde‐derived iminium ions 1 form benzoxacyclic products 2 in a photochemical reaction cascade ( n= 0, 1). Structurally different products 3 ( meta photocycloaddition) and 4 (aza Paternò–Büchi reaction) are observed depending on two key substituents (R, R 1 ).