NEW MATERIAL:A 6,7-dimethyl-2,3-dicarboxy-5-hydroxy-7-(2-substituted-1-methyl- ethyl)bicyclo[4,3,0]nona-2,4-diene shown by formula I [R is CH2OR2 (R2 is H or OH-protecting group) or COOR3 (R3 is H or carboxyl-protecting group); R1 is H or carboxyl-protecting group].

EXAMPLE: 6,7-Dimethyl-2,3-bis(methoxycarbonyl)-5-hydroxy-7-(3-t-butyl-diphenylsi lyloxy-1-methyl-propyl)bicyclo[4,3,0]nona-2,-9-diene.

USE: A promoting substance of hatch of nematode nits, having strong hatch pro moting action on nematode nits living in plants.

PREPARATION: A compound shown by formula II (R4 is alkyl) is oxidized with an organic peracid to give a compound shown by formula III and the epoxide is converted into methyl group to give a compound shown by formula I.