Versatile reactivity of a zwitterionic isolable silylene toward ketones: silicon-mediated, regio- and stereoselective C-H activation.
Reactions of the isolable, ylide-like silylene LSi: (1) (L = CH[(C=CH(2))CMe][N(Ar)](2), Ar = 2,6-iPr(2)C(6)H(3)) with different ketones (benzophenone, benzylideneaceton, acetophenone) have been investigated. The metastable dearomatized siloxindane 2, which was suggested previously as reaction intermediate but could not be detected in related reactions, has been obtained for the first time from the regio- and stereoselective addition of silylene 1 to benzophenone at low temperature. By variation of the reaction temperature, the initial product 2 rearranges under re-aromatization stereoselectively to the corresponding siloxindane 3, which has also been isolated in high yield. In contrast, reactions of 1 with benzylidenacetone and acetophenone furnish the [4+1] cycloaddition product 4 and the silyl enol ether 5, respectively. It is proposed that in all reactions the 1,4-dipolar nature of 1 plays key role, leading to highly reactive donor-acceptor adducts, which undergo rearrangement (tautomerization) to the final products. The new compounds 2, 3, 4, and 5 were characterized by (1)H, (13)C, and (29)Si NMR spectroscopy, EI-MS, and elemental analysis, and their structures determined by single-crystal X-ray diffraction analysis.
Xiong
Yun
Y
Technische Universitaet Berlin, Institute of Chemistry: Metalorganic and Inorganic Materials, Sekr. C2, Strasse des 17. Juni 135, 10623 Berlin, Germany.
Yao
Shenglai
S
Driess
Matthias
M