Cyclization routes for the synthesis of functionalized pyrano[2,3-b ]indolones, pyrazolo[3,4-b]indoles, and furo[2,3-b]indoles

Abstract

The synthesis of biologically active core structures containing pyrano[2,3-b]indol-2(9H)-ones, pyrano[2,3-b]indol-4(9H)-ones, pyrazolo[3,4-b]indoles, and furo[2,3-b]indoles are described. Pyrano[2,3-b]indol-2(9H)-ones are synthesized by three different metal-free syntheses (DCC, DMSO; CDI, DBU, CH2Cl2; or Mukaiyama's reagent, Et3N, MeCN) and pyrano[2,3-b]indol-4(9H)-ones are prepared by one-pot or two-step synthesis. Pyrazolo[3,4-b]indoles are synthesized by Fischer indole type cyclization and McMurry coupling is employed for the synthesis of furo[2,3-b]indoles. All these core structures are synthesized from simple, common 3-acetylindol-2-ols. © Georg Thieme Verlag Stuttgart - New York.