A novel reaction mode in the cycloaddition of thermally generated silylenes with conjugated dienes

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