AbstractThe stability of α‐ (1) and β‐asarone (2) in ethanolic solutions (30 %; 100 %; pH 7; pH3) was studied under daylight conditions over a period of six months. After rapid initial light‐induced isomerization of 1 to 2, a number of (i) oxidation products, i.e. 2,4,5‐trimethoxybenzaldehyde (4); l‐(2,4,5‐trimethoxyphenyl) propan‐2‐one (5); 2,4,5‐trimethoxypropiophenone (6); and (ii) addition products, i.e. l‐ethoxy‐l‐(2,4,5‐trimethoxyphenyl) propane (3); (1R, 2R; 1S, 2S)‐l‐ethoxy‐l‐(2,4,5‐trimethoxyphenyl) propan‐2‐ol (7A); (1R, 2S; 1S, 2R)‐l‐ethoxy‐l‐(2,4,5‐trimethoxy‐phenyl propan‐2‐ol (7B); (1R, 2R; 1S, 2S)‐l‐(2,4,5‐trimethoxyphenyl) propan‐1, 2‐diol (8A); (1R, 2S; 1S2R)‐1‐(2,4,5‐trimethoxyphenyl) propan‐1,2‐diol (8B); as well as (iii) the dimers l‐(2′,4′,5′‐trimethoxyphenyl)‐2‐methyl‐3‐(2,4,5‐trimethoxyphenyl)‐lE‐pentene (9) and l‐(2′,4′,5′‐trimethoxyphenyl)‐2‐methyl‐3‐ethyl‐lα, 2β, 3α (H)‐4,6,7‐trimethoxyindane (13) were detected after extractive sample preparation. In addition, three dimers, l‐(2′,4′,5′‐trimethoxyphenyl)‐2‐methyl‐3(2,4,5‐trimethoxyphenyl)‐penta‐1E, 4‐diene (10); 1 ‐(2′,4′,5′‐trimethoxyphenyl)‐2‐(2,4,5‐trimethoxyphenyl)‐3,4‐dimethylcyclobutane (11) and l‐(2′,4′,5′‐trimethoxyphenyl)‐2‐rnethyl‐3‐(2,4,5‐trimethoxyphenyl) prop‐l‐en‐3‐one (12) were tentatively identified. Identifications were carried