Tris(trimethylsilyl)silyllithium (3) reacted with aldehydes and ketones (molar ratio 2 : 1) according to a modified Peterson mechanism under formation of transient silenes, which were immediately trapped by excess 3 to give the organolithium derivatives (Me 3 Si) 3 SiSi(SiMe 3 ) 2 C(Li) Ŕ1 R 2 (7). Hydrolysis of 7 afforded the alkylpolysilanes (Me 3 Si) 3 SiSi(SiMe 3 ) 2 CHR 1 R 2 (8). Depending on the substituents R 1 and R 2 , 7 proved to be rather unstable in THF solution and underwent a rapid rearrangement, involving a 1,3-Si,C-trimethylsilyl migration, resulting in the formation of the lithium silanides (Me 3 Si) 2 Si(Li)Si(SiMe 3 ) 2 C(SiMe 3 )R 1 R 2 (9), which were hydrolized during the aqueous workup to give the H-silanes (Me 3 Si) 2 Si(H)Si(SiMe 3 ) 2 C(SiMe 3 )R 1 R 2 (10). Reaction of 9 with chlorotrimethylsilane produced the 1-trimethylsilylalkylpolysilanes (Me 3 Si) 3 SiSi(SiMe 3 ) 2 C(SiMe 3 )R 1 R 2 (11). The structures of the products described were elucidated by comprehensive spectral analyses. The results of X-ray crystal structure analyses, performed for 8 l (R 1 = H, R 2 = 2,4,6-(MeO) 3 C 6 H 2 ), 10 d (R 1 = H, R 2 = Mes) and 11 d (R 1 = H, R 2 = Mes) are discussed and confirm the expected extreme sterical congestion of the molecules.