An efficient synthesis of cycloalkane-1,3-dione-2-spirocyclopropanes from 1,3-cycloalkanediones using (1-aryl-2-bromoethyl)-dimethylsulfonium bromides: Application to a one-pot synthesis of tetrahydroindol-4(5H)-one

An efficient synthesis of cyclohexane- and cyclopentane-1,3-dione-2-spirocyclopropanes from 1,3-cycloalkanediones using sulfonium salts was achieved. The reaction of 1,3-cycloalkanediones with (1-aryl-2-bromoethyl)-dimethylsulfonium bromides and powdered K₂CO₃ in EtOAc provided the corresponding spirocyclopropanes in high yields. Furthermore, a one-pot synthesis of tetrahydroindol-4(5H)-one from 1,3-cyclohexanedione was achieved using the present protocol and a sequential ring-opening cyclization of spirocyclopropane with a primary amine.