A Simple and Efficient Synthesis of Highly Substituted Indeno[1,2-b]pyrrole and Acenaphtho[1,2-b]pyrrole Derivatives by Tandem Three-Component Reactions

A green, convenient and tandem procedure for the efficient synthesis of highly substituted indeno[1,2-b]pyrrole and acenaphtho[1,2-b]pyrrole derivatives by domino three-component reaction of tryptamine/benzylamine, 1,3-dicarbonyl compounds and ninhydrin/ acenaphthenequinone is described. The significant features of this procedure were characterized by mild reaction conditions, high yields, operational simplicity and it being environmentally benign.

Melting points were recorded on an Electrothermal digital melting point apparatus and uncorrected. IR Spectra were recorded on a Nicolet FT-IR500 spectrophotometer using KBr optics. 1 H NMR and 13 C MNR spectra were recorded on a JMTC-400/54/SS spectrometer using DMSO-d6 as solvent and TMS as internal standard. HRMS analyses were conducted on a Bruker micro-TOF-Q-MS analyzer.
X-Ray diffraction data were made on a Rigaku Mercury CCD area detector with graphite monochromated Mo-Ka radiation.

Typical experimental procedure for 4
A mixture of an equimolar amount of 1,3-dicarbonyl compound 2 (0.5 mmol) and tryptamine 3 (0.5 mmol) was stirred in ethanol at room temperature for 1h. Ninhydrin 1 (0.5 mmol) was then added to this solution and stirred at room temperature for 0.5-1h. Completion of the reaction was monitored with TLC, the mixture was poured into cold water, then filtered and washed with EtOH (95%). The precipitate was purified by recrystallization from EtOH to give the product 4.

Typical experimental procedure for 6
A mixture of an equimolar amount of 1,3-dicarbonyl compound 2 (0.5 mmol) and tryptamine 3 (0.5 mmol) was stirred in ethanol at room temperature for 1h.
Acenaphthenequinone 5 (0.5 mmol) was then added to this solution and stirred at room temperature for 0.5-1h. Completion of the reaction was monitored with TLC, the mixture was poured into cold water, then filtered and washed with EtOH (95%).
The precipitate was purified by recrystallization from EtOH to give the product 6.

Typical experimental procedure for 8
A mixture of an equimolar amount of 1,3-dicarbonyl compound 2 (0.5 mmol) and benzylamine 7 (0.5 mmol) were stirred in ethanol at room temperature for 2h.
Ninhydrin 1 (0.5 mmol) was then added to this solution and stirred at room temperature for 0.5-1h. Completion of the reaction was monitored with TLC, the reaction mixture was poured into ice cold water. Then, the addition of brine solution to the reaction mixture brought the precipitate. The precipitate was filtered, washed with water to give the product 8. The crystal for X-ray diffraction was developed by recrystallization from EtOH.