The thermal LiHal elimination of ▪- and ▪ functional compounds provides a simple synthetic route to four-membered SiC and SiN rings. In attempts to inhibit dimerisation sterically, bulky silylmethyl and silylamino substituents were introduced (I–III). (Me 3Si) 3CSiF 2R reacts with LiNHR′, 1,3- migration of a silyl group from carbon to the nitrogen (I, R′= 2,4,6-Me 3C 6H 2) taking place. Substitution occurs for R′ = SiMe 2CMe 2, (II, III) only. Dichloro-bis(trimethylsilyl)methane reacts with halogenosilanes and lithium in THF to give bis(trimethylsilyl)-halogenosilaethanes (Me 3Si) 2CHSi(Hal)RR′; R= Me, R′ = N(SiMe 3) 2, IV, Hal = F; V, Hal = Cl. However a reductive THF cleavage accompanied by a silyl group migration to the oxygen occurs and 1-halogenosilyl-1- trimethylsilyl-5-trimethylsiloxi-pent-1-ene,(Me 3Si)(RR′SiHal)CCH(CH 2) 3OSiMe 3, Are The main products (VII–X) of these reactions. Disubstitution occurs with F 3Si-i-Pr (VI). (Me 3Si) 3CSiFNHSiMe 2CMe 3 (II) reacts with C 4H 9Li in a molar ratio 1 2 to give an 1-aza-2,3-disilacyclobutane (XI), involving substitution, LiF elimination, and nucleophilic migration of a methanide ion of the unsaturated precusor. (Me 3Si) 2CHSiFMeN (2,4,6-Me 3C 6H 2)SiMe 3 cyclizes under comparable conditions in the reaction with MeLi via a methylene group of the mesityl group (XII).