Photoinduced Rearrangement of Aryl‐Substituted Acylcyclohexasilanes

Abstract

AbstractIn the present study, we examined photochemical transformations of acylcyclohexasilanes (Me3Si)2Si6Me12(Me3Si)COR (compounds 1) with aromatic substituents attached to the carbonyl C atom. When photolyzed at wavelengths above 300 nm in hydrocarbon solvents, 1a–c (1a: R = o‐Tol; 1b: R = 2,3‐Me2C6H3; 1c: R = 2,4‐Me2C6H3) afforded the previously unknown eight‐membered heterocyclopolysilanes 3a–c, which feature endocyclic Si=C double bonds with remarkable selectivity. If two ortho‐alkyl groups are present at the aromatic ring (compounds 1d–f), the primary products of type 3 (3d: R = Mes; 3e: R = 1,6‐Me2C6H3; 3f: R = 2,4,6‐iPr3C6H2) are photochemically unstable and undergo intramolecular C–H‐bond addition reactions of a ortho‐CH3 group to the Si=C double bond, which leads to the formation of spirobenzocyclobutenes. When photolysis was performed in the presence of methanol, the expected 1,2‐addition products (compounds 4) of the Si=C double bond were obtained quantitatively in all cases. 4a (R = o‐Tol) and 4b (R = Mes) were isolated by crystallization from acetone and fully characterized spectroscopically and by single‐crystal X‐ray diffraction analysis. Interestingly 4b was obtained as an isomeric mixture arising from syn and anti addition of methanol to the endocyclic Si=C bond, whereas the syn addition was observed exclusively in the case of 4a.