[en] The cyclobutane compounds 2, 3, 4 or 5, which represent in position-15 functionalized gibberellin derivatives, reacted with ³H₂O under mild alkaline conditions in a retroaldol-like cleavage to give diacetyl[15-³H]gibberellin-A₃-7-aldehyde (6) and the isomeric compound 7. In respect of a second possibility of 15-tritiation, diacetyl-GA₃-7-aldehyde (1) was irradiated with UV-light in benzene/³H₂O to form diacetyl[15α-³H]GA₃-7-aldehyde (6a). Oxidation and deacetylation of 6 afforded [15-³H]gibberellin-A₃(8). (author)