1,4-Addition of Indoles to Enones Catalyzed by Nanocrystalline TiO₂

Significance

Nanocrystalline-TiO₂-catalyzed 1,4-addition of indoles to enones was developed. Indoles 1 reacted with enones 2 in CH₂Cl₂ in the presence of nanocrystalline TiO₂ to give the corresponding C-adducts 3 in 75-93% yield, exclusively (eq. 1). One-pot 1,4-1,2-addition of indoles and TMSCN to enones was also achieved. After the treatment of indoles 1 with enones 2 in the presence of nanocrystalline TiO₂, TMSCN was added to the reaction mixture to afford the corresponding silylated cyanohydrin derivatives 4 in 54-73% yield (eq. 2). The nanocrystalline TiO₂ catalyst can be used for five cycles without significant loss of catalytic activity.