3,6-Dihydro-5H-pyrazolo [4 ',3 ':5,6]pyrano[3,4-b] indol-5-one

Pyrano [3,4-b]indol-1(9H)-ones and indolo [2,3-c]coumarins are important classes of heterocyclic compounds with versatile biological activities. Herein, we describe a straightforward and scalable synthesis of 3,6-dihydro-5H-pyrazolo [4',3':5,6]pyrano [3,4-b]indol-5-one, a pyrazolo-fused pyrano [3,4-b]indolone, via a three step approach including Fischer-indole synthesis and intramolecular esterification. The compound is fully characterized by means of H-1 and C-13 NMR spectra, using direct and long-range heteronuclear correlation experiments (HMBC and HMQC).