That's interesting. Now we only need to see how hard it is to synthesize the tricyclic starting material 2:
The 4,9-dihydropyrano[3,4-b]indol-1(3H)-ones (2) necessary for the following reactions can be either obtained out of ?-valerolactone by reaction with oxalyl ester, followed by reaction with diazotized aniline (Japp–Klingemann-reaction),13 or out of ?-butyrolactone and oxalyl esters, respectively, following hydrolysis and reaction with phenylhydrazones, as described previously.14
13. Lehmann, et. al, Arch. Pharm. Pharm. Med. Chem. 1987, 320, 1202–1209.
14. Lehmann, et. al, Arch. Pharm. Pharm. Med. Chem. 1987, 320, 698–704.