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

Abstract While 2‐alk‐ω‐enyloxy‐sustituted benzaldehydes do not display any photochemical reactivity at the arene core, 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 found: (a) Most commonly, reaction led benzoxacyclic products in which olefin tether underwent a formal, yet unprecedented carboformylation (13 examples, 44–99 % yield). The cascade process occurred with high diastereoselectivity and was be stereoconvergent. (b) If substituent resides 3‐position of benzene ring, meta photocycloaddition observed produced tetracyclic skeletons five stereogenic centers excellent regio‐ (2 58–79 (c) internally substituted alkene, an avoided azetidine formed aza Paternò–Büchi 95–98