Imino-Diels-Alder Adducts. Part XIII. Polymorphism in Pyrano [3,2-c] Quinolines |
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Authors: | Krishnan Ravikumar Balasubramanian Sridhar Masna Mahesh Vaddu Venkata Narayana Reddy |
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Affiliation: | (1) Laboratory of X-ray Crystallography, Indian Institute of Chemical Technology (IICT), Room No. 150, Hyderabad , 500 007, India;(2) Organic Chemical Division-II, Indian Institute of Chemical Technology, Hyderabad , 500 007, India |
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Abstract: | Abstract Crystallization by slow evaporation of methanol solution of 5-(4-nitrophenyl)-3,4,4a5,6,10b-hexahydro-2H-pyrano[3,2-c] quinoline, yields two polymorphs. Rectangle plate-like crystals have a triclinic (P ) structure, with one molecule in the asymmetric unit, a = 8.2299(5) ?, b = 9.7774(6) ?, c = 11.0047(7) ?, α = 65.718(1)°, β = 75.699(1)° and γ = 71.617(1)°, while, long needle-like crystals exhibit a monoclinic (C2/c) crystal structure in which two independent molecules comprise the asymmetric unit, a = 32.285(3) ?, b = 9.4045(7) ?, c = 22.804(2) ? and β = 114.965(1)°. The crystal structures reveal the molecule in both the polymorphs as an endo-Imino-Diels-Alder cycloadduct isomer. The stereochemistry of the pyran ring in both the polymorphs is exo to the quinoline ring formed in the cycloaddition step. The molecules are linked by N–H···O hydrogen bonds into centrosymmetric dimers forming R2 2(18) rings in the triclinic form, while they are arranged to form a helical chain in the monoclinic form. Index abstract Crystallization by slow evaporation of methanol solution of 5-(4-nitrophenyl)-3,4,4a5,6,10b-hexahydro-2H-pyrano[3,2-c] quinoline, yields two polymorphs. The crystal structures reveal the molecule in both the polymorphs as an endo-Imino-Diels-Alder cycloadduct isomer. The stereochemistry of the pyran ring in both the polymorphs is exo to the quinoline ring formed in the cycloaddition step. The molecules are linked by N–H···O hydrogen bonds into centrosymmetric dimers forming R2 2(18) rings in the triclinic form, while they are arranged to form a helical chain in the monoclinic form. In the present study, we have determined the crystal structures of two polymorphs of pyranoquinoline, I and II. |
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Keywords: | Pyranoquinolines Diels-Alder cycloadducts Crystal structure Polymorphs Hydrogen bonding |
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