A thermally generated silylene bearing bulky substituents, Tbt(Mes)Si: (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl] phenyl; Mes = 2,4,6-trimethylphenyl), reacted with isoprene at room temperature to give the corresponding 2-vinylsilirane, which thermally isomerized to the corresponding 3-silolene, while silylene underwent competitive [1+2] and [1+4] cycloadditions with 2,4-dimethyl-1,3-butadiene.