AbstractThe reaction between 1′,3′,3′‐trimethylspiro[2H‐1‐benzopyran‐2,2′‐indoline] and its derivatives (3a‐e) and 1,1‐bis[4‐(dimethylamino)phenyl]ethylene (“Michler's ethylene”) (4) were studied. Depending on the reaction time, the isomeric products 2,2‐bis[4‐(dimethylamino)phenyl]‐4‐{2‐methylidene‐1,3,3‐trimethylindoline}chromans (7a‐e) or 1′,3′,3′‐trimethyl‐4‐{2,2‐bis[4‐(dimethyl‐amino)phenyl]vinyl}‐spiro[chroman‐2,2′‐indolines](8a‐d) were obtained. With deuterium labelled “Michler's ethylene” and deuterated solvents the mechanism of this reaction was confirmed. Reaction of the 2,2‐bis[4‐(dimethylamino)phenyl]‐2H‐chromenes10c,dand 1,3,3‐trimethyl‐2‐methylene‐indoline (9) furnished the dihydrospiropyrans8c,d. Chromene10cand 1,1‐bis(p‐methoxyphenyl)‐ethylene gave 2.2‐bis(4‐methoxyphenyl)‐4‐ [2,2‐bis[4‐(dim