Abstract The thermal decomposition of hexamethylsilirane in the presence of selected disubstituted acetylenes (Me 3 SiC CSiMe 3), Me 2 HSiC CSiMe 2 H, Me 3 SiC CCH 3, Me 3 SiC CCMe 3, Me 3 CC CCH 3) resulted in Me 2 Si addition to the C C bonds to give the respective silacyclopropenes. These are thermally stable but are extremely reactive toward atmospheric oxygen and moisture and react readily with methanol and ethanol at ...