THE THERMAL-ISOMERIZATION OF A TETRAHYDRO-2,3-DISILANAPHTHALENE INTO A 1,2-DISILACYCLOBUTANE - THE CONVERSION OF A FORMAL SILENE [2+4]CYCLODIMER INTO THE [2+2]CYCLOADDUCT

2,2,3,3-tetrak(trimethylsilyl)-2,3-dilanaphthalene (3), the formal [24] cyclodimer of the transient 2-mesityl-1,1-bis(trimethylsilyl)-silen e (2), on thermal treatment gradually isomerizes to give a mixture of the [2+2] products (E)- and - predominantly - 2,2-tetrakis(trimethylsi lyl)-1,2-disilacyclobutane [(E/Z)-4]. By prolonged heating or at highe r temperatures both (E/Z)-3 and (2)-4 are converted into (E)-4, the th ermodynamically most stable head-to-head dimer of 2. Possible pathways of the isomerization processes are discussed.