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Photochemistry of o-allyloxy-/crotyloxyacetophenones (6a,b) has been investigated under different conditions. Irradiation of 6a,b in dry benzene, under N2 atmosphere (Pyrex filter), led to the isolation of (syn)-2-ethenyl/propenyl-3-hydroxy-3-methyl-2,3-dihydrobenzofurans (7a,b∼10%) as the sole product. Irradiation of 6a,b in dry benzene in the presence of 0.1–0.4 mol equiv. of triethylamine resulted in slightly increased formation of 7a,b, besides pinacols (9 and 10) and triethylamine addition products (11 and 12). However, the formation of 7a,b is suppressed with increasing molar ratios of triethylamine, with increased formation of products (9–13). On the other hand, irradiation of 6a,b in dry acetonitrile results in the formation of both syn-(7a,b) as well as anti-isomers of benzodihydrofuranols (8a,b), besides some highly unexpected intramolecular arene-olefin addition products (14–16); formation of these intramolecular arene–olefin addition products is quenched in the presence of 0.1 mol equiv. of triethylamine. With increasing molar ratios of triethylamine, in acetonitrile solvent, the formation of 7, 8 is also suppressed with increased formation of products (9–13) derived from photoreduction of carbonyl function through electron transfer from TEA. No product derived from intramolecular interaction of the ketone derived anion radical/ketyl radical with an olefinic moiety has been detected. A plausible mechanistic rationalization of the results obtained is presented. [Copyright &y& Elsevier]

UV irradiation of (E,E)-arylidene-β-ionones 1 leads to photoisomerization resulting in (Z,E) arylidene-β-ionones 2, which undergo electrocyclization to 1,7,7-trimethyl-3-(E-2′-arylethenyl)-2-oxabicyclo[4.4.0]deca-3,5-dienes 3, and the latter in the excited state add regioselectively, involving only the electron-rich endocyclic diene, to molecular oxygen affording highly stable endoperoxides 6. [Copyright &y& Elsevier]

Reactions of 2-(N-methylanilino)-3-formylchromones with a number of bifunctional nucleophiles, involving substitution of N-methylanilino moiety and/or condensations with 3-formyl function have provided an easy access to a variety of potentially biologically active hetero-annelated chromones, novel macrocycles, and tetradentate ligands having intact chromone moiety. [Copyright &y& Elsevier]