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Synlett 2005(20): 3055-3058  
DOI: 10.1055/s-2005-921921
LETTER
© Georg Thieme Verlag Stuttgart · New York

Three-Component Coupling Strategy for Expeditious Synthesis of 4-Aminobenzoxazinones on Mineral Support

Lal Dhar S. Yadav*, Ritu Kapoor
Department of Chemistry, University of Allahabad, Allahabad - 211002, India
e-Mail: lds-yadav@hclinfinet.com;
Further Information

Publication History

Received 4 September 2005
Publication Date:
28 November 2005 (online)

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Abstract

Novel montmorillonite K-10 clay supported three-­component reactions of substituted salicylaldehydes, N-substituted ureas/carbamates and ammonium acetate or an amine expeditiously yield 3,4-dihydro-4-amino-2H-benz[e]-1,3-oxazin-2-ones via ­cycloisomerization of intermediate aldimines under solvent-free microwave irradiation in a one-pot procedure.

Key words

multi-component reactions - mineral support - microwaves - solvent-free - 4-aminobenzoxazinones

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A CEM Discover Focused Microwave Synthesis System operating at 2450 MHz was used at an output of 560 W for all the experiments. The temperature (85 ± 5 °C) was monitored by a built-in infrared sensor and the irradiation time was set at 2 min.

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General Procedure for the Synthesis of 3,4-Dihydro-4-amino-3-aryl-2 H -benz[ e ]-1,3-oxazin-2-ones 8a-u. To a solution of salicylaldehyde 1 (5 mmol) and substituted aryl/alkylurea 2 (5 mmol) in a small amount of CH2Cl2 (10 mL) was added ammonium acetate or aniline (5 mmol) and montmorillonite K-10 clay (0.50 g) mixed thoroughly and dried under reduced pressure. The contents were taken in a 100 mL conical flask and subjected to MW irradiation at 560 W for 2 min. The reaction mixture was then thoroughly mixed outside the MW oven for 2 min and again irradiated for another 2 min. This intermittent irradiation mixing cycle was repeated for a total irradiation time (Table [2] ). After completion of the reaction as indicated by TLC (hexane-EtOAc, 8:2, v/v), the product was extracted with CH2Cl2 (3 × 80 mL), the extract was filtered and the filtrate was evaporated under reduced pressure to leave the crude product which was recrystallized from EtOH to give an analytically pure sample of 8 as yellowish needles.

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Characterization Data for Representative Compounds.
Compound 8a: yellowish needles; mp 125-126 °C. IR (KBr): ν = 3360, 3000, 1715, 1592, 1570, 1449 cm-1. 1H NMR (400 MHz, DMSO-d 6 ): δ = 3.06 (br s, 2 H, exchanges with D2O), 6.75 (t, 1 H, J = 8.0 Hz), 7.19-7.87 (m, 9 H). 13C NMR (100 MHz, DMSO-d 6 ): δ = 78.0, 113.1, 114.2, 118.6, 120.3, 122.6, 129.0, 129.4, 130.2, 150.0, 166.4, 177.0. MS (EI): m/z = 240 [M+]. Anal. Calcd for C14H12N2O2: C, 69.99; H, 5.03; N, 11.66. Found: C, 69.89; H, 5.23; N, 11.46.
Compound 8h: yellowish needles; mp 116-117 °C. IR (KBr): ν = 3364, 3012, 1700, 1592, 1571, 1450 cm-1. 1H NMR (400 MHz, DMSO-d 6 ): δ = 2.31 (s, 3 H), 3.05 (br s, 2 H, exchanges with D2O), 6.75 (t, 1 H, J = 7.9 Hz), 7.14-7.84 (m, 8 H). 13C NMR (100 MHz DMSO-d 6 ): δ = 21.2, 78.2, 113.0, 114.0, 118.2, 120.5, 122.5, 128.7, 129.5, 130.4 150.1, 166.0, 177.0. MS (EI): m/z = 254 [M+]. Anal. Calcd for C15H14N2O2: C, 70.85; H, 5.55; N, 11.02. Found: C, 70.55; H, 5.85; N, 10.82.
Compound 8r: yellowish needles; mp 210-211 °C. IR (KBr): ν = 3370, 3016, 1720, 1598, 1577, 1454 cm-1. 1H NMR (400 MHz, DMSO-d 6 ): δ = 1.09 (t, 3 H, J = 6.8 Hz), 2.57 (q, 2 H, J = 6.8 Hz), 3.09 (br s, 2 H, exchanges with D2O), 6.79 (t, 1 H, J = 8.0 Hz), 7.86 (d, 1 H, J = 2.5 Hz), 8.23 (d, 1 H, J = 2.5, 2.5 Hz). 13C NMR (100 MHz, DMSO-d 6 ): δ = 13.9, 58.5, 78.9, 118.6, 122.4, 129.5, 130.7, 150.6, 166.3, 177.3. MS (EI): m/z = 350 [M+]. Anal. Calcd for C10H10N2O2Br2: C, 34.32; H, 2.88; N, 8.00. Found: C, 34.42; H, 3.18; N, 8.10.,