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Synthesis 2006(12): 1995-2004  
DOI: 10.1055/s-2006-942388
PAPER
© Georg Thieme Verlag Stuttgart · New York

Interesting Results of Catalytic Hydrogenation of 3-(2-Nitrophenyl)isoxazoles and 3-(Nitrophenyl)-4,5-dihydroisoxazoles [1]

V. Singha, S. Madapaa, G. P. Yadavb, P. R. Maulikb, S. Batra*a
a Medicinal Chemistry Division, Central Drug Research Institute, PO Box 173, Lucknow 226001, India
Fax: +91(522)2623405, 2623938; e-Mail: batra_san@yahoo.co.uk;
b Molecular and Structural Biology Divisions, Central Drug Research Institute, PO Box 173, Lucknow 226001, India
Further Information

Publication History

Received 20 December 2005
Publication Date:
08 May 2006 (online)

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Abstract

The palladium-on-carbon assisted hydrogenolysis of substituted 3-(2-nitrophenyl)isoxazoles, irrespective of substitution on the isoxazole ring, invariably leads to reduction of the nitro to the amino group with concomitant regiospecific ring closure to yield substituted 4-aminoquinolines. In contrast similar hydrogenation of 3-(2-, 3-, and 4-nitrophenyl)-4,5-dihydroisoxazoles (2-isoxazolines) results in reduction of the nitro group only with conservation of the dihydroisoxazole ring to yield the corresponding 3-(aminophenyl)-4,5-dihydroisoxazoles.

Key words

isoxazole - 4-aminoquinoline - hydrogenation - ring transformation - regiospecific

1

CDRI Communication no 8402. A part of this work was presented as a poster at the CSIR-ACS conference OCCB-2006 at NCL Pune from 7-9th January, 2006.

1

CDRI Communication no 8402. A part of this work was presented as a poster at the CSIR-ACS conference OCCB-2006 at NCL Pune from 7-9th January, 2006.

19

Crystal data of compound 7d: C10H9N3O, M = 187.2; orthorhombic, P212121, a = 5.710 (1), b = 9.925 (1), c = 16.153 (3) Å, V = 915.4 (3) Å3, Z = 4, D c = 1.358g cm-3, µ (Mo-Kα) = 0.09 mm-1, F(000) = 392.0, colorless block, crystal dimensions 0.225 × 0.175 × 0.150 mm, 1370 reflections measured (R int = 0.019), 1230 unique, R = 0.0456 [(Δ/σ)max = 000)], wR 2 = 0.1087 for 1270 on F 2 values of reflections with I>2σ(I), S = 1.028 for all data and 128 parameters. Unit cell determination and intensity data collection (2θ = 50°) were performed on a Bruker P4 diffractometer at 293 (2) K. Structure solutions was performed by direct methods and refinements by full-matrix least-squares methods on F 2. Programs: XSCANS [Siemens Analytical X-ray Instrument Inc.: Madison, WI, USA, 1996) was used for data collection and data processing], SHELXTL-NT [(Bruker Axs Inc.: Madison, Wisconsin, USA 1997) was used for structure determination, refinements and molecular graphics]. Further details of the crystal structure investigation can be obtained from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK (CCDC deposition no. of compound 7d: 297540.