Intramolecularly donor-stabilized silenes: Part 6. The synthesis of 1-[2,6-bis(dimethylaminomethyl)phenyl]silenes and their reaction with aromatic aldehydes

The intramolecularly donor-stabilized silenes ArR1SiC(SiMe3)2 (3a–d) (3a: R1 = Me; 3b: R1 = t-Bu; 3c: R1 = Ph; 3d: R1 = SiMe3; Ar = 2,6-(Me2NCH2)2C6H3) were prepared by treatment of the (dichloromethyl)oligosilanes (Me3Si)2R1Si–CHCl2 (1a–d), with 2,6-bis(dimethylaminomethyl)phenyllithium (molar ratio 1:2). For 3c and 3d, X-ray structural analyses were performed indicating that only one dimethylamino group of the tridentate ligand is coordinated to the electrophilic silene silicon atoms, i.e., the central silicon atoms are tetracoordinated. The N → Si donation leads to pyramidalization at the silene silicon atoms; the configuration at the silene carbon atoms is planar. For a chemical characterization 3a and 3c were treated with water to give the silanols ArR1Si(OH)–CH(SiMe3)2 (5a,c). Studies of the reactions of 3a and 3c with benzaldehyde, 4-chlorobenzaldehyde or 4-methoxybenzaldehyde, respectively, revealed an unexpected reaction path leading to the substituted 2-oxa-1-sila-1,2,3,4-tetrahydronaphthalenes 12a, 12c, 13 and 14. Both 12a and 12c were structurally characterized by X-ray analyses. The formation of these six-membered cyclic compounds, which is discussed in detail, gives support to a dipolar mechanism for the general reaction of silenes with carbonyl derivatives.

Graphical abstractThe intramolecularly donor-stabilized silenes ArRSiC(SiMe3)2 (R = Me, Ph; Ar = 2,6-(Me2NCH2)2C6H3), easily accessable by treatment of (dichloromethyl)bis(trimethylsilyl)silanes with 2,6-bis(dimethylaminomethyl)phenyllithium (1:2), react with aromatic aldehydes to give substituted 2-oxa-1-sila-1,2,3,4-tetrahydronaphthalenes. The formation of these cyclic products provides interesting information on the general mechanism of the reaction of silenes with carbonyl compounds.Figure optionsDownload full-size imageDownload as PowerPoint slide