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Synlett 2023; 34(13): 1631-1633
DOI: 10.1055/a-2017-4176
letter

Formamidine-Induced Translocative Rearrangement of 2-Pyrones to 2-Pyridone Analogues with a 1,5-Diketo Motif

Rajan Kumar
,
Ashoke Sharon  ∗
The authors acknowledge SERB, Delhi, for financial support (EMR/2017/003331)
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Abstract

A new formamidine-induced translocative rearrangement of 2-pyrone analogues into 2-pyridone derivatives with a 1,5-diketo motif was identified. All the products were characterized by spectroscopic analysis. In addition, single-crystal X-ray structural studies of two molecules were performed.

Key words

ring transformation - rearrangement - pyrones - pyridones - diketones - medicinal chemistry

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/a-2017-4176. Included are the experiment procedure and characterization data of final compounds.
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Publication History

Received: 26 November 2022

Accepted after revision: 21 January 2023

Accepted Manuscript online:
21 January 2023

Article published online:
14 March 2023

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  • 16 Compounds 2a–g; General Procedure Formamidine acetate (0.45 g, 4.35 mmol) and KOH (0.83 g, 14.5 mmol) were dissolved in anhyd DMF, and the resulting mixture was stirred for 10–15 min under N2. The appropriate pyrancarboxamide 1a–g (1 g, 2.9 mmol) was added and the resulting mixture was stirred at rt for 6–8 h. When the reaction was complete [TLC; Rf = 0.5 (30% EtOAc–hexane)], the mixture was poured into ice-cooled water and the precipitate was collected by filtration. The filtrate, which contained some product, was extracted with EtOAc (3 × 20 mL), and the organic layer was dried (Na2SO4) and concentrated under reduced pressure. The precipitate and the extracted crude from the organic layer were combined and then purified by column chromatography (silica gel, EtOAc–hexane). 5-Benzoyl-4-(methylsulfanyl)-2-oxo-N-phenyl-1,2-dihydropyridine-3-carboxamide (2a) White powder; yield: 70%; mp 235–238 ℃; IR (KBr): 1658 (C=O), 3089 (NH) cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 2.19 (s, 3 H, SMe), 7.02–7.06 (m, 1 H, ArH), 7.28–7.32 (m, 2 H, ArH), 7.51–7.56 (m, 3 H, ArH), 7.62–7.67 (m, 3 H, ArH), 7.76–7.78 (m, 2 H, ArH), 10.42 (s, 1 H, NH), 12.32 (s, 1 H, NH). 13C NMR (100 MHz, DMSO-d 6): δ = 18.0, 119.5, 120.1, 124.9, 129.4, 129.5, 129.9, 130.2, 134.5, 137.0, 138.5, 139.2, 150.2, 159.6, 163.9, 193.5. HRMS (ESI): m/z [M + H]+ calcd for C20H17N2O3S: 365.0954; found: 365.0933. 5-Benzoyl-N-(3-methylphenyl)-4-(methylsulfanyl)-2-oxo-1,2-dihydropyridine-3-carboxamide (2b) Yellow powder; yield: 75%; mp 165–167 ℃. IR (KBr): 1666 (C=O), 3332 (NH) cm–1. 1H NMR (400 MHz, DMSO-d 6): δ = 2.19 (s, 3 H, SMe); 2.25 (s, 3 H, Me); 6.85–6.87, (m, 1 H, ArH); 7.15–7.19 (m, 1 H, ArH); 7.39–7.41 (m, 1 H, ArH); 7.49–7.56 (m, 4 H, ArH); 7.63–7.67 (m, 1 H, ArH); 7.76–7.78 (m, 2 H, ArH), 10.36 (s, 1 H, NH); 12.32 (s, 1 H, NH). 13C NMR (100 MHz, DMSO-d 6): δ = 18.2, 21.7, 116.8, 120.1, 124.7, 129.3, 129.9, 130.1, 133.9, 137.7, 138.5, 139.0, 139.5, 148.8, 159.4, 163.4, 192.6. HRMS (ESI): m/z [M + H]+ calcd for C21H19N2O3S: 379.1111; found: 379.1085.