Abstract The thioxophosphole 6 undergoes Diels-Alder reaction with the triazolindiones 7a and b to the adducts 8a and b. Analogously 11a and b are formed from the selenoxophosphole 9 and the maleic acid derivatives 10a and b. The triazolindion reactions of 6, 9 and also of 12 suffer considerably under the presence of water. Apart from elemental sulfur and selenium on the one hand phosphole oxides (15) such as secundary products ...