Synthesis of 5-aryl-2-piperidino-5 H -chromeno[3,4-c ]pyridine--1-carbonitriles

4-Chloro-2-aryl-2 H -3-chromenecarbaldehydes 3a-g on reaction with malononitrile in ethanol in the presence of piperidine gave 5-aryl-2-piperidino-5 H -chromeno[3,4-c ]pyridine-1-carbonitriles 4a-g in good yields.

2][13] We also reported the synthesis of 9-amino-6H-benzo[c]chromene-8,10-dicarbonitriles by the reaction of 2H-3-chromenecarbaldehydes with malononitrile and piperidine. 14In this present paper we report the results of the reaction of 4-chloro-2-aryl-2H-3-chromenecarbaldehydes 3a-g with malononitrile in ethanolpiperidine wherein there is formation of pyridine ring fused to chromene with the participation of piperidine as a nucleophile during the pyridine ring formation.
The mechanism of the formation of 5-aryl-2-piperidino-5H-chromeno [3,4-c]pyridine-1carbonitriles 4a-g is shown in Scheme 2. The first step is the nucleophilic substitution of the labile Cl by the malononitrile.A facile intramolecular nucleophilic attack by the nitrogen of CN on the CHO group leads to cyclic intermediate 6a-g.It is reaction with nucleophile piperidine, followed by loss of H2O results in pyridine ring derivatives 6a-g.In several literature methods of pyridine synthesis, piperidine is used the solvent and acts as a base. 16,17However, in the present reaction the piperidine is incorporated into the product structure.The structure of 4a is confirmed from single crystal X-ray analyses (Figure 1).
This work reports a new synthesis of pyridine fused to chromene, starting from the β-chloroacrolein moiety in the chromene and malononitrile in piperidine

Experimental Section
General.All melting points were determined on a Polmon digital melting point apparatus (Model No. MP-96).IR spectra were recorded on a FT-IR Perkin-Elmer 1605 spectrophotometer using KBr discs and UV spectra were recorded on a Schimadzu UV-VIS 1601 spectrophotometer.The 1 H NMR (200 MHz) and 13 C NMR (50.3 MHz) spectra were recorded on a Varian Gemini Unity Spectrometer in CDCl3 using TMS as internal standard (chemical shifts in  ppm).Mass spectra were recorded on a VG micromass 7070H instrument.Elemental analyses were performed on an Elemental Vario El instrument.XRD were recorded on a Bruker Smart Apex CCD area detector on a D8 goniometer.
One of the authors (M.Venkati) thanks the CSIR, New Delhi for financial support and grant of SRF.Our sincere thanks to the Director, IICT, Dr. J.S. Yadav, Hyderabad, India for providing spectral data and library facilities