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 Li t Bu. The [2 + 2] cycloaddition to imines yields Si, Si 1‐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/anti 1‐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, Si 1‐dichloro‐substituted silanimine Cl 2 SiN t Bu ( 24 ) is formed. This can be trapped by Me 3 SiOMe or Ph 2 CN t Bu 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 Cl 2 SiNR derivatives.