Variously substituted 2‐vinylpyrroles underwent an endo‐addition [4+2] cycloaddition reaction with maleimides followed by a spontaneous highly diastereoselective (93–98% de) isomerization to give tetrahydroindoles in moderate to excellent yield. Treatment with activated MnO2 in refluxing toluene provided the corresponding indoles in moderate to good yield. This highly convergent methodology for formation of indoles is versatile and the starting materials are conveniently prepared. J. Heterocyclic Chem., (2009).

N‐p‐Toluenesulfonyl‐3‐vinylpyrrole underwent endo‐addition [4 + 2] cycloaddition reactions with maleimides and benzoquinones, followed by isomerization to give tetrahydroindoles in good yields. Dehydrogenation with activated MnO2 in refluxing toluene gave the corresponding indoles in fair to good yields. Detosylation via saponification or with magnesium in refluxing methanol gave the N‐H indoles in moderate to good yields. This method for formation of indoles is both convergent and versatile and uses starting materials that are conveniently prepared. J. Heterocyclic Chem., (2009).

A series of 108 tetrahydroindoles has been prepared by a one‐pot synthesis from 2‐alkylpyrroles, cyclic ketones, maleimides, and an acid catalyst. A 5‐vinylpyrrole is formed by an acid‐catalyzed condensation of a 2‐alkyl‐substituted pyrrole with a ketone, which is subsequently trapped in situ by a maleimide in a predominantly endo‐addition Diels‐Alder reaction. Isomerization of the double bond into the pyrrole ring gives a tetrahydroindole with predominant cis‐fusion of the cycloalkane ring. J. Heterocyclic Chem., 46, 503 (2009).

Melting points were measured with a Mel-Temp apparatus, and were not corrected or calibrated. Rf values obtained using SiO2 in 1:2 EtOAc:hexane. Infrared spectra were collected on a Thermo Fisher Scientific Nicolet iS5 spectrophotometer. 1 H NMR and 13 C NMR spectra were recorded on AV-500 Bruker Avance III HD, HD-500 Bruker Avance III HD, or AM-400 Bruker Avance III HD spectrometers at ambient temperature and are referenced to the solvent.Mass spectra were recorded on a Bruker Biotof II instrument using poly(ethylene glycol) as an internal calibrant, or on an Agilent 7890B gas chromatograph using an Agilent DB-5MS 250 µm capillary column with an Agilent 7200 GC/QTOF-MS detector calibrated with external perfluorotributylamine. Reagents and solvents were used as purchased. General procedures Method A: Reactions of indole with acetophenones in ethanolic HCl at RTIndole 1a (0.234 g, 2.00 mmol, 1 eq), naphthalene 10 (0.064 g, 0.50 mmol, 0.25 eq), and acetophenone 8a-h (3.00 mmol, 1.5 eq) were dissolved in ethanol (10 mL). Concentrated hydrochloric acid (1 mL) was added dropwise at room temperature. The resulting solution was allowed to stirred at RT for 5 d. The reaction mixture was neutralized using sat. sodium bicarbonate (25 mL) and the organic layer was extracted with dichloromethane (4 × 25 mL). The combined organic extracts were dried with magnesium sulfate, filtered, and excess solvent was removed with a rotary evaporator. The resulting mixtures were analyzed using 1 H NMR spectroscopy, with naphthalene as the internal integration standard. The crude mixture was dry-S2 loaded onto silica gel and the products were purified by column chromatography or MPLC using EtOAc:hexane as the eluent. Method B: Reactions of indole with acetophenones in ethanolic HCl at 40 o CThis procedure is identical with Method A, except reactions were stirred at 40 o C for 3 d before neutralization. Method C: Reactions of indole with acetophenones in refluxing acetic acidIndole 1a (1.171g, 10.00 mmol, 1eq) and acetophenone 8a-h (12.00 mmol, 1.2 eq) were dissolved in acetic acid (1 mL) and then refluxed overnight. The reaction mixture was neutralized using sat. sodium bicarbonate (10 mL) and the organic layer was extracted with dichloromethane (4 × 25 mL). The combined organic extracts were dried with magnesium sulfate, filtered, and excess solvent was removed with a rotary evaporator. The crude mixture was dry-loaded onto silica gel and purified by column chromatography using EtOAc:hexane as the eluent, giving products 11a-h. S32:1 condensation products: Bisindoles (11a-h) 3,3'-(1-phenylethane-1,1-diyl)bis(1H-indole) (11a) [46] was prepared by Method A from 8a (361 mg) as a white crystalline powder; 130 mg, 37% (calcd by 1 H NMR); mp 118-120 o C (lit.

in Wiley InterScience (www.interscience.wiley.com).Variously substituted 2-vinylpyrroles underwent an endo-addition [4þ2] cycloaddition reaction with maleimides followed by a spontaneous highly diastereoselective (93-98% de) isomerization to give tetrahydroindoles in moderate to excellent yield. Treatment with activated MnO 2 in refluxing toluene provided the corresponding indoles in moderate to good yield. This highly convergent methodology for formation of indoles is versatile and the starting materials are conveniently prepared.