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Synlett 2018; 29(07): 874-879
DOI: 10.1055/s-0036-1591534
letter
© Georg Thieme Verlag Stuttgart · New York

l-Proline: An Efficient Organocatalyst for the Synthesis of 5-Substituted 1H-Tetrazoles via [3+2] Cycloaddition of Nitriles and Sodium Azide

Saket B. Bhagat 
Department of Pharmaceutical Sciences & Technology, Institute of Chemical Technology, Matunga (E), Mumbai 400 019, India   Email: vikastelvekar@rediffmail.com
,
Vikas N. Telvekar*
Department of Pharmaceutical Sciences & Technology, Institute of Chemical Technology, Matunga (E), Mumbai 400 019, India   Email: vikastelvekar@rediffmail.com
› Author Affiliations
Further Information

Publication History

Received: 16 November 2017

Accepted after revision: 02 January 2018

Publication Date:
07 February 2018 (online)

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Abstract

A simple and efficient route for the synthesis of a series of 5-substituted 1H-tetrazoles using l-proline as a catalyst from structurally diverse organic nitriles and sodium azide is reported. The prominent features of this environmentally benign, cost effective, and high-yielding l-proline-catalyzed protocol includes simple experimental procedure, short reaction time, simple workup, and excellent yields making it a safer and economical alternative to hazardous Lewis acid catalyzed methods. The protocol was successfully applied to a broad range of substrates, including aliphatic and aryl nitriles, organic thiocyanates, and cyanamides.

Keywords

5-substituted 1H-tetrazoles - organic nitriles - thiocyanates - cyanamides - sodium azide - l-proline

Supporting Information

    Supporting information for this article (included are experimental details, 1H NMR and 13C NMR analysis of the synthesised compounds) is available online at https://doi.org/10.1055/s-0036-1591534.
  • Supporting Information
 

  • References and Notes

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  • 34 Typical Procedure for the Synthesis of 5-Substituted 1H-tetrazoles 3, 5, 7 General Procedure for the Synthesis of 5-Aryl/Alkyl 1H-Tetrazoles 3 The mixture of organic nitrile (1 mmol), NaN3 (1.25 mmol), and l-proline (30 mol%) in DMF (5 mL) was stirred at 110 °C for 1–2 h. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was allowed to cool to room temperature. The cooled reaction mixture was poured in ice water (15 mL) with stirring. The resulting mixture was acidified with dilute HCl under vigorous stirring. The solid product was filtered under suction and washed with sufficient cold water. The solid was air dried to obtain the pure product. General Procedure for the Synthesis of 5-(Substituted ­Sulfanyl)-1H-tetrazoles 5 The mixture of appropriate thiocyanate (1 mmol), NaN3 (1.25 mmol), and l-proline (30 mol%) in n-propanol (5 mL) was refluxed for 1–2 h. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was allowed to cool to room temperature. The cooled reaction mixture was poured in ice water (15 mL) with stirring. The resulting mixture was acidified with dilute HCl under vigorous stirring. The solid product was filtered under suction and washed with sufficient cold water. The solid was air dried to obtain the pure product. General Procedure for the Synthesis of 5-Arylamino-1H-tetrazoles 7 The mixture of organic cyanamide (1 mmol), NaN3 (1.25 mmol), and l-proline (30 mol%) in DMF (5 mL) was stirred at 110 °C for 1–2 h. The progress of the reaction was monitored by TLC. After completion of the reaction, the reaction mixture was allowed to cool to room temperature. The cooled reaction mixture was poured in ice water (15 mL) with stirring. The resulting mixture was acidified with dilute HCl under vigorous stirring. The solid product was filtered under suction and washed with sufficient cold water. The solid was air dried to obtain the pure product. 5-Phenyl-1H-tetrazole (3a, Table 2 Entry 1) Yield 96%, 140.3 mg; white solid; mp 214–216 °C (lit.6a 215–216 °C). IR (KBr): νmax = 3207, 3075, 3051, 1610, 1565, 1491, 1466, 688 cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 16.8 (br, NH), 8.03–8.01 (m, 2 H), 7.62–7.58 (m, 3 H) ppm. 13C NMR (100 MHz, DMSO-d 6): δ = 155.1, 131.2, 129.5, 126.8, 124.1 ppm. MS (ESI): m/z = 147 [M + H]+. 5-(4-Pyridyl)-1H-tetrazole (3j, Table 2, Entry 10) Yield 94%, 138.3 mg; white solid; mp 254–256 °C (lit.21 254–255 °C). IR (KBr): νmax = 3485, 3264, 3099, 3040, 2966, 1621, 1580, 1450, 1388, 1123, 1096, 1042, 1022, 845, 784 cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 16.30 (br s, 1 H), 8.51 (d, J = 7.6 Hz, 2 H), 7.78 (d, J = 7.6 Hz, 2 H) ppm. 13C NMR (100 MHz, DMSO-d 6): δ = 159.1, 149.9, 139.4, 120.9 ppm. MS (ESI): m/z: 148 [M + H]+. 5-(Benzylsulfanyl)-1H-tetrazole (5b, Table 3, Entry 2) Yield 93%, 178.8 mg; white solid; mp 133–135 °C (lit.35 134–135 °C). IR (KBr): νmax = 3061, 2900, 2812, 2653, 2545, 2490, 1532, 1493, 1454, 1433, 1362, 1318, 1236, 1079, 1037, 980, 776, 704 cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 16.45 (br s, 1 H), 7.40–7.38 (m, 2 H), 7.32–7.28 (m, 3 H), 4.50 (s, 2 H) ppm. 13C NMR (100 MHz, DMSO-d 6): δ = 154.2, 137.2, 129.5, 129.1, 128.2, 36.5 ppm. MS (ESI): m/z = 193 [M + H]+. 5-(p-Tolyl)amino-1H-tetrazole (7b, Table 4, Entry 2) Yield 86%, 150.7 mg; coffee colored solid; mp 200–202 °C (lit.35 201–203 °C). IR (KBr): νmax = 3268, 3210, 3135, 3091, 1626, 1578, 1545, 1470, 1440, 1256, 1134, 1090, 1060, 835, 782, 730, 503 cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 15.21 (br s, 1 H), 9.66 (s, 1 H), 7.38 (d, J = 8.4 Hz, 1 H), 7.12 (d, J = 8.4 Hz, 1 H), 2.24 (s, 1 H) ppm. 13C NMR (100 MHz, DMSO-d 6): δ = 155.8, 138.1, 130.2, 124.0, 117.8, 20.3 ppm. MS (ESI): m/z = 176 [M + H]+. 5-(4-Chlorophenyl)amino-1H-tetrazole (7d, Table 4, Entry 4) Yield 89%, 174.1 mg; white solid; mp 227–229 °C (lit.35 226–228 °C). IR (KBr): νmax = 3268, 3210, 3135, 3091, 1626, 1578, 1545, 1470, 1440, 1256, 1134, 1090, 1060, 835, 782, 730, 503 cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 15.43 (br s, 1 H), 9.97 (s, 1 H), 7.56–7.53 (d, J = 11.9 Hz, 1 H), 7.38–7.35 (d, J = 11.9 Hz, 1 H) ppm. 13C NMR (100 MHz, DMSO-d 6): δ = 156.1, 139.8, 129.3, 125.1, 118.7 ppm. MS (ESI): m/z = 196 [M + H]+.