Silaheterocyclen, XXIII. Synthese und Thermolyseverhalten von Si‐funktionellen 2‐Silaazetidinen

Silaheterocycles, XXIII[1]. – Synthesis and Thermolysis Reactions of Si‐Functionalized 2‐Silaazetidines Dichloroneopentylsilene (1) is formed in situ by the reaction of trichlorovinylsilane with LitBu. The [2 + 2] cycloaddition to imines yields Si, Si1‐dichloro‐functionalized 2‐silaazetidines in a preparative scale. With aldimines as trapping agents for 1, the resulting SiN four‐membered ring compounds are isolated as syn/anti1‐isomers (e.g. syn/anti‐15 and ‐16; syn/anti ≈︁ 2:1). Silene 1 is not liberated from the silaazetidines on heating, but the Si, Si1‐dichloro‐substituted silanimine Cl2SiNtBu (24) is formed. This can be trapped by Me3SiOMe or Ph2CNtBu to give the addition products 25 and 26, respectively. The pathways are discussed which lead to stereoisomeric SiN ring compounds by a multiple‐step mechanism including zwitterionic intermediates (1,4‐dipoles). In addition there is strong evidence for the formation of 1, depending on the trapping reagent used. This fact may be explained by donor→silene interactions. The thermolysis products of silaazetidines support the formulation of a stepwise decomposition to an alkene and Cl2SiNR derivatives.