Palladium-catalyzed domino Heck-disilylation and -borylation of alkene-tethered 2-(2-halophenyl)-1H-indoles: access to diverse disilylated and borylated indolo[2,1-a]isoquinolines†
The chemoselective reaction remains a tremendous but particularly fascinating challenge in organic synthesis. Herein, we report a new domino Heck/disilylation reaction of alkene-tethered 2-(2-halophenyl)-1H-indoles with hexamethyldisilane under palladium catalysis. This procedure involving the formation of one C–C bond and two C–Si bonds proceeds efficiently through two key steps of the chemoselective Heck reaction and C–H activation by overcoming undesirable C3–H bond activation on the indoles, thus generating various disilylated tetracyclic indolo[2,1-a]isoquinolines in moderate to excellent yields. Furthermore, borylated indolo[2,1-a]isoquinolines can be produced by a Heck/borylation cascade.