NEW MATERIAL:A 1-benzazocine derivative of formula I (R1 and R3 are lower alkoxyl; R2 is lower alkyl; R4 is aralkyl; R5 and R6 are H, lower alkoxyl or together may have hydroxymethine or lower alkylenedithio bond; X is O, methine or bonding group of formula II at the linked site of X; Y is O or two hydrogen atoms).

EXAMPLE: 1-Benzyl-4, 5-dihydro-8, 10-dimethoxy-9-methyl-1-benzazocine-2, 6(1H, 3H)-dione.

USE: A medicine having a pharmacological action such as analgesic action.

PROCESS: A cyclopent[b]indole derivative of formula III is irradiated with light from a light source such as a halogen lamp in a suitable solvent, e.g. methanol, to give the compound of formula I.