ChemInform Abstract: FeCl₃‐Mediated Friedel—Crafts Hydroarylation with Electrophilic N‐Acetyl Indoles for the Synthesis of Benzofuroindolines.

Abstract

This provides an efficient access towards chromenoindolines and benzofuroindolines, a unique motif in diazonamide, bipleiophylline and azonazine. -(BEAUD, R.; GUILLOT, R.; KOUKLOVSKY, C.; VINCENT*, G.; Angew. Chem., Int. Ed. 51 (2012) 50, 12546-12550, http://dx.doi.org/10.1002/anie.201206611 ; Inst. Chim. Mol. Mater., Univ. Paris-Sud, F-91405 Orsay, Fr.; Eng.) -Nuesgen 19-123

External oxidant-free electrooxidative [3 + 2] annulation between phenol and indole derivatives

“…In analogous to the natural bias, the oxidative [3 + 2] annulation between phenols and indoles usually gives benzofuro[2,3-b]indolines. Over the past decade, different reaction protocols for the synthesis of benzofuro[2,3-b]indoline moiety have been developed by Harran 37 , 40 , Danishefsky 41 , Vincent 42 , 43 , and others 44 – 46 . In contrast, attempts on phenol–indoles coupling for the synthesis of benzofuro[3,2-b]indolines have rarely succeeded 47 .…”

Two-Carbon Ring Expansion of Cyclobutanols to Cyclohexenones Enabled by Indole Radical Cation Intermediate: Development and Application to a Total Synthesis of Uleine

“…7 An alternative and traceless way to reverse the indole polarity consists of its single-electron transfer (SET) oxidation to a radical cation. 8 Steckhan, Blechert, and co-workers reported in the 1990s that indoles, upon UV irradiation, underwent a facile triphenylpyrylium tetrafluoroborate (TPPT)-catalyzed Diels−Alder cycloaddition with electron-rich dienes and invoked a radical cation intermediate to account for the reaction outcome. 9 In spite of the elegance of this pioneering work, the chemistry of the indole radical cation remained dormant for almost 20 years.…”

“…16 Since the benzylic (C3) radical is easily oxidizable, we reasoned that it might be possible to exploit this peculiar reactivity of indole in which C2 and C3 act sequentially as electrophilic centers allowing therefore two consecutive 1,2-alkyl migrations 17 and set out to examine the conversion of 1-(1H-indol-2-yl)cyclobutan-1-ols 1 to 2,3,4,9-tetrahydro-1H-carbazol-1-ones 2 (Scheme 2b). The tetrahydrocarbazolone motif is found in many bioactive natural products such as uleine (5) 18 and dasycarpidone (6) 18 and bioactive compounds such as GJP14 (7) 19 and GSK983 (8). 20 Although the radical addition/oxidation/semipinacol rearrangement sequence converting 1-vinylcyclobutan-1-ols to functionalized cyclopentanones under photoredox catalytic conditions is known, 21 the two-carbon ring-expansion process via a radical cation intermediate remains to be exploited.…”

Translating planar heterocycles into 3D analogs via photoinduced hydrocarboxylation

“…Intermolecular indole hydrofunctionalization reactions remain limited despite the indole C2-C3 pbond being prone to dearomative processes. 14,[28][29][30][31][32] Established indole dearomative functionalization strategies rely on intramolecular nucleophiles or difunctionalization via delivery of two specific groups across the p-system. [12][13][14][15][16] Formal hydrocarboxylation of indole is currently accomplished via lithiation- carboxylation-hydrogenation sequences, resulting in poor chemoselectivity that largely precludes implementation in complex settings.…”

“…47 Substitution at the site of CO2 substituted carbon center (28) was nonetheless formed in sufficient quantities to enable early stage medicinal chemistry efforts. Furthermore, a tricyclic substrate bearing both C2 and C3 substitution underwent efficient hydrocarboxylation (29), presumably due to strain release upon radical addition.…”