Synlett 2018; 29(04): 477-482
DOI: 10.1055/s-0036-1591725
letter
© Georg Thieme Verlag Stuttgart · New York

2-Phenyl-2,3-dihydrobenzo[d]thiazole: A Mild, Efficient, and Highly Active in situ Generated Chemoselective Reducing Agent for the One-Pot Synthesis of 5-Monoalkylbarbiturates in Water

Subarna Jyoti Kalita
Department of Chemistry, University of Gauhati, G. B. Nagar, Guwahati 781014, Assam, India   Email: dcdeka@rediffmail.com
,
Dibakar Chandra Deka*
Department of Chemistry, University of Gauhati, G. B. Nagar, Guwahati 781014, Assam, India   Email: dcdeka@rediffmail.com
› Author Affiliations
Further Information

Publication History

Received: 15 October 2017

Accepted: 24 October 2017

Publication Date:
28 November 2017 (online)


Abstract

A metal- and catalyst-free reductive alkylation protocol for the one-pot synthesis of 5-monoalkylbarbiturates from barbituric acids and aldehydes using the in situ generated chemoselective reducing agent 2-phenyl-2,3-dihydrobenzo[d]thiazole from 2-aminothiophenol and benzaldehyde is described. The notable advantages of the protocol are operational simplicity, mild reaction conditions, high yield, short reaction time, and simple workup and purification process which make it highly attractive.

Supporting Information

 
  • References and Notes

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  • 24 General Procedure for the Synthesis of 5-Monoalkylbarbiturates 4aa–cp A mixture of barbituric acid 1 (1 mmol) and aldehyde 2 (1 mmol) was refluxed in 5 mL of water for an appropriate time until the generation of 5-arylidenebarbituric acid as indicated by TLC. Next 2-aminothiophenol (3, 1 mmol) and benzaldehyde (2a, 1 mmol) were added, and the reaction mixture was further refluxed for an appropriate time. On completion of the reaction as indicated by TLC the reaction mixture was allowed to cool to room temperature and was extracted with EtOAc (3 × 10 mL). After drying with anhydrous Na2SO4 and evaporation under reduced pressure, the crude product was purified suitably either by recrystallization from a DCM/EtOH (1:1) solvent mixture or column chromatography on silica gel using EtOAc/hexane (2:8) as the eluent to afford 5-monoalkylbarbiturate 4. 5-Benzylpyrimidine-2,4,6(1H,3H,5H)-trione (4aa) White solid; 0.191 g (88%); mp 209–210 °C. 1H NMR (300 MHz, DMSO-d 6): δ = 3.22–3.24 (m, 2 H), 3.87–3.90 (m, 1 H), 7.05–7.24 (m, 5 H), 11.17 (s, 2 H) ppm. 13C NMR (75 MHz, DMSO-d 6): δ = 33.3, 49.3, 126.7, 128.3, 128.9, 137.4, 150.6, 170.0 ppm. IR (KBr): νmax = 3234, 2939, 1716, 1681, 1581 cm–1. ESI-MS: m/z calcd for C11H10N2O3 +: 218.07; found: 219.0 [M + H]+. Anal. Calcd (%) for C11H10N2O3: C, 60.55; H, 4.62; N, 12.84. Found: C, 60.70; H, 4.46; N, 13.02. 5-Cinnamyl-6-hydroxypyrimidine-2,4(1H,3H)-dione (4ah) Pale yellow sticky solid; 0.195 g (80%). 1H NMR (300 MHz, DMSO-d 6): δ = 2.68 (d, 2 H, J = 7.2 Hz), 5.99–6.09 (m, 1 H), 6.27 (s, 1 H), 6.41 (d, 1 H, J = 15.9 Hz), 7.19–7.31 (m, 5 H), 11.28 (s, 2 H) ppm. 13C NMR (75 MHz, DMSO-d 6): δ = 43.0, 75.0, 121.5, 126.2, 127.7, 128.4, 128.7, 134.3, 136.5, 150.0, 171.6 ppm. IR (KBr): νmax = 3234, 3030, 2974, 1734, 1680, 1616, 1560 cm–1. ESI-MS: m/z calcd for C13H12N2O3 +: 244.08; found: 245.0 [M + H]+. Anal. Calcd (%) for C13H12N2O3: C, 63.93; H, 4.95; N, 11.47. Found: C, 64.08; H, 5.07; 11.29. 1,3-Dimethyl-5-(thiophen-2-ylmethyl)pyrimidine-2,4,6(1H,3H,5H)-trione (4cn) Pale yellow solid; 0.226 g (90%); mp 118–119 °C. 1H NMR (300 MHz, CDCl3): δ = 3.20 (s, 6 H), 3.72 (s, 3 H), 6.76–6.77 (m, 1 H), 6.85–6.88 (m, 1 H), 7.12–7.13 (m, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 28.4, 30.7, 50.4, 125.2, 127.0, 127.2, 136.4, 151.0, 167.7 ppm. IR (KBr): νmax = 2976, 1672, 1589 cm–1. ESI-MS: m/z calcd for C11H12N2O3S+: 252.06; found: 253.0 [M + H]+. Anal. Calcd (%) for C11H12N2O3S: C, 52.37; H, 4.79; N, 11.10. Found: C, 52.22; H, 4.94; 10.98. 1,3-Dimethyl-5-(naphthalen-1-ylmethyl)pyrimidine-2,4,6(1H,3H,5H)-trione (4cp) White solid; 0.266 g (90%); mp 153–154 °C. 1H NMR (300 MHz, CDCl3): δ = 2.92 (s, 6 H), 3.91 (s, 3 H), 7.22 (t, 1 H, J = 6.9 Hz), 7.33 (t, 1 H, J = 7.8 Hz), 7.47–7.53 (m, 2 H), 7.75 (d, 1 H, J = 8.4 Hz), 7.82 (d, 1 H, J = 8.1 Hz), 7.94 (d, 1 H, J = 8.4 Hz) ppm. 13C NMR (75 MHz, CDCl3): δ = 28.1, 34.7, 50.8, 123.2, 124.9, 125.8, 126.3, 127.7, 128.6, 128.9, 131.4, 131.5, 133.7, 150.9, 168.6 ppm. IR (KBr): νmax = 3953, 1695, 1658, 1560 cm–1. ESI-MS: m/z calcd for C17H16N2O3 +: 296.12; found: 297.1 [M + H]+. Anal. Calcd (%) for C17H16N2O3: C, 68.91; H, 5.44; N, 9.45. Found: C, 68.76; H, 5.60; N, 9.63.
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  • 29 CCDC 1574477 contains the supplementary crystallographic data for compound 4cn. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.