Reaction of 3-(1-arylsulfonylalkyl)-indoles with easily enolisable derivatives promoted by potassium fluoride on basic alumina

Active methylene compounds and nitro derivatives react with 3-(1-arylsulfonylalkyl)-indoles in the presence of potassium fluoride on basic alumina at room temperature leading to the corresponding adducts in good yields. Under basic conditions, sulfonylindoles suffer elimination of arenesulfinic acid leading to an intermediate vinylogous imine that promptly adds stabilized carbanions. The obtained 3-indolyl derivatives are pivotal intermediates for the synthesis of indole-based alkaloids and amino acids.