FIGURE 4. Protecting-group-free total synthesis of fischerindole I (5) and welwitindolinone A (4).

Reagents and conditions as follows. a, Indole (2.0 equiv.), LiHMDS (3.3 equiv.), THF, -78 °C, 30 min, copper(II)-2-ethylhexanoate (1.5 equiv.), -78 to 23 °C, 20 min, 62%. b, Montmorillonite K-10 clay, microwave irradiation at 120 °C, 6 min, 57% b.r.s.m. c, NH₄OAc (40 equiv.), NaCNBH₃ (7.5 equiv.), 3 Å molecular sieves, MeOH/THF, sonication, 18 h, 42%. d, HCO₂H (2.0 equiv.), CDMT (2.2 equiv.), DMAP (0.1 equiv.), NMM (2.2 equiv.), DCM, 23 °C, 30 min; Et₃N (17.5 equiv.), COCl₂ (2.0 equiv.), DCM, 0 °C, 10 min, 95%. e, DDQ (2.5 equiv.), H₂O, THF, 0 °C, 30 min, 92%. f, XeF₂, H₂O, MeCN, 23 °C, 5 min; 44%. DDQ, 2,3-dichloro-5,6-dicyanobenzoquinone; MeCN, acetonitrile. For selected physical data for compounds 18, 5 and 4 see the Supplementary Information.