Redox-triggered dearomative[5+1]annulation of indoles with O-alkyl ortho-oxybenzaldehydes for the synthesis of spirochromanes

The dearomative[5+1]annulation of 2-methylindoles with new five-membered synthons O-alkyl orthooxybenzaldehydes was developed unprecedentedly through cascade[1,5]-hydride transfer/dearomativecyclization in HFIP for the synthesis of spirochromanes bearing the 2-methylindolenine skeleton.Inaddition,the dual alkylation of the methyl group of 2-methylindolenines was achieved by sequential operation through the redox neutral[5+1]annulation with the second five-membered synthon N-alkylortho-aminobenzaldehyde,providing the chromane and tetrahydroquinoline fused spiroindolenines ingood yields.Furthermore,the auxiliary group that facilitates the hydride transfer process could be simplyremoved.