2 , 4-Diamino-5-( nitromethyl )-5 H-chromeno [ 2 , 3-b ] pyridine-3-carbonitrile

Dimethyl sulfoxide (DMSO) is a cheap polar aprotic solvent used in organic synthesis and in pharmacology because of its low cost, high stability, and non-toxicity. Multicomponent reactions (MCRs) are highly convergent processes and have good atom, step, and pot economies. In this communication, the multicomponent transformation of salicylaldehyde, malononitrile dimer, and nitromethane in DMSO at room temperature was investigated to give 2,4-diamino-5-(nitromethyl)5H-chromeno[2,3-b]pyridine-3-carbonitrile in good yield. The structure of the earlier unknown compound was confirmed by means of elemental analysis, mass-, nuclear magnetic resonance, and infrared spectroscopy.


Introduction
Sustainable trends in chemistry are gaining momentum [1]. Organic chemistry is becoming "greener", it reduces waste and uses more effective approaches. Dimethyl sulfoxide (DMSO) meets modern challenges in organic chemistry as it has aprotic properties, it is eco-friendly and it simplifies the treatment of a reaction mixture. Thus, it may be one of the most effective solvents today.
Multicomponent reactions (MCRs) are highly convergent processes that include two or more chemical reactions. These processes are often related to the PASE principles-atom, step, and pot economies [2]. Such a convergence leads to the formation of several bonds at once and, thus, to high bond-forming index (BFI) of the whole process [3]. Apparently, the mentioned advantages of MCRs in corporation with advantages of DMSO as a solvent are supposed to be even more effective, eco-friendly and useful for the development of new synthetic approaches [4]. In the literature, there is not a very large variety of multicomponent reactions in DMSO. In general, these are reactions in the iodine-DMSO system [5][6][7].
We also carried out the transformation described above in other aprotic solvents and catalyst-solvent systems developed by us (Table 1).
We also carried out the transformation described above in other aprotic solvents an catalyst-solvent systems developed by us (Table 1).
In aprotic polar solvents, the reaction proceeds with good yields ( When the reaction in DMSO was completed, water was added to the reaction mixture and the final chromeno[2,3-b]pyridine 4 was crystallized in pure form. Compound 4 was synthesized in 73% yield. We also carried out the transformation described above in other aprotic solvents and catalyst-solvent systems developed by us (Table 1). In aprotic polar solvents, the reaction proceeds with good yields ( The BFI (bond-forming index) of this transformation was four since four new bonds were formed in one stage, namely 2 C-C bonds, 1 C-N, and 1 C-O bonds.
The structure of novel chromeno[2,3-b]pyridine 4 was confirmed by 1 H, 13 C NMR, and IR spectroscopy data, mass spectrometry data and elemental analysis (see Supplementary Materials). Only one set of signals was recorded in 1 H and 13 C-NMR spectra.
The first stage of the process was a rapid formation of Knoevenagel adduct 5 with the expulsion of a hydroxide anion [25]. This hydroxide anion instantly catalyzed a rapid Pinner cyclization of adduct 5 into intermediate 6. Then, the Michael addition of nitromethane 3 occurred to form anion B. Next, there were successive tautomerizations and Pinner-type cyclization to the final 2,4-diamino-5-(nitromethyl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile 4.
The melting point was measured with Gallenkamp melting-point apparatus (Gallenkamp & Co., Ltd., London, UK). 1 H and 13 C-NMR spectra were recorded in DMSO-d6 temperature. IR spectrum was registered with a Bruker ALPHA-T FT-IR spectrometer (Bruker Corporation, Billerica, MA, USA) in KBr pellets. The MS spectrum (EI = 70 eV) was obtained directly with a Kratos MS-30 spectrometer (Kratos Analytical Ltd., Manchester, UK). For elemental analysis, a 2400 Elemental Analyzer (Perkin Elmer Inc., Waltham, MA, USA) was used.
The melting point was measured with Gallenkamp melting-point apparatus (Gallenkamp & Co., Ltd., London, UK). 1 H and 13 C-NMR spectra were recorded in DMSO-d 6 temperature. IR spectrum was registered with a Bruker ALPHA-T FT-IR spectrometer (Bruker Corporation, Billerica, MA, USA) in KBr pellets. The MS spectrum (EI = 70 eV) was obtained directly with a Kratos MS-30 spectrometer (Kratos Analytical Ltd., Manchester, UK). For elemental analysis, a 2400 Elemental Analyzer (Perkin Elmer Inc., Waltham, MA, USA) was used.

Conclusions
The title compound, 2,4-diamino-5-(nitromethyl)-5H-chromeno[2,3-b]pyridine-3carbonitrile, was synthesized in good yield using the mild and efficient multicomponent method with simple implementation and equipment and available starting materials. The new synthesized compound was characterized by spectroscopic methods (NMR, IR and MS-EI), and elemental analysis.