Thermal and photochemical reactions of naphtho[1,2,3,4‐ def ]chrysene with 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione

The thermal and photochemical reactions between naphtho‐[1,2,3,4‐ def ]chrysene ( 1 ) and 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 2 ) have been compared. In the thermal reaction, 2 electrophilically attacks 1 to give substitution product 4 which in part is further transformed into 5 and 6 . In the light‐induced reaction, 2 predominantly undergoes [4π + 2π] cycloaddition to 1 with subsequent loss of hydrogen to yield 6 which then photodecomposes to give a complex mixture containing 10. 5 exists in two atropisomeric forms. The structure of one form, 5b , was determined by X‐ray crystallography.