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DOI: 10.1055/s-0035-1561411
Alkyl and Aryl 4,5-Dichloro-6-oxopyridazin-1(6H)-carboxylates: A Practical Alternative to Chloroformates for the Synthesis of Symmetric and Asymmetric Carbonates
Publikationsverlauf
Received: 06. Januar 2016
Accepted after revision: 09. Februar 2016
Publikationsdatum:
07. März 2016 (online)
Abstract
Symmetric and asymmetric carbonates were synthesized by using alkyl or aryl 4,5-dichloro-6-oxopyridazin-1(6H)-carboxylates. Five aryl 4,5-dichloro-6-oxopyridazin-1(6H)-carboxylates were converted into the corresponding diaryl carbonates in good to excellent yields by treatment with potassium carbonate in refluxing THF. When the 4,5-dichloro-6-oxopyridazin-1(6H)-carboxylates were treated with aliphatic or aromatic alcohols in the presence of potassium tert-butoxide in toluene at room temperature, they gave the corresponding symmetric or asymmetric carbonates in moderate to excellent yields. Alkyl and aryl 4,5-dichloro-6-oxopyridazin-1(6H)-carboxylates are therefore efficient, stable, and ecofriendly alternatives to chloroformates.
Key words
pyridazines - alcohols - phenols - carbonates - alkoxycarbonylations - acyl-transfer agentsSupporting Information
- Supporting information for this article is available online at http://dx.doi.org/10.1055/s-0035-1561411.
- Supporting Information
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References and Notes
- 1 These authors contributed equally to this work.
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- 8 Symmetric Carbonates 2a–e ; General Procedure Using Potassium Carbonate K2CO3 (1.0 mmol) was added to a solution of the appropriate pyridazine 1 (1.0 mmol) in THF (20 mL), and the mixture was allowed to reflux until pyridazine 1 was consumed (TLC). The solvent was evaporated under reduced pressure, and the symmetric carbonates 2a–e were isolated by column chromatography [silica gel (2.5 × 3 cm), CH2Cl2]. Once the desired product had been isolated, the column was eluted with EtOAc to isolate 4,5-dichloropyridazin-3(2H)-one, which was obtained quantitatively and reused. Diphenyl Carbonate (2) White solid; yield: 193 mg (80%); mp 75–76 °C. IR (KBr): 3058, 1773, 1592, 1490, 1255, 1233, 1182, 1071, 1016, 996, 751, 685, 501 cm–1. 1H NMR (300 MHz, DMSO-d 6): δ = 7.30–7.35 (m, 2 H), 7.40–7.51 (m, 8 H). 13C NMR (75 MHz, DMSO-d 6): δ = 121.2, 126.4, 129.7, 150.7, 151.7. HRMS (EI): m/z [M+] calcd for C13H10O3: 214.0630; found: 214.0634. Symmetric (2) or Asymmetric (4 and 6) Carbonates; General Procedure Using Potassium tert-Butoxide Alcohol 3 or 5 (0.84 mmol) was added to a solution of the appropriate pyridazine 1 (0.7 mmol) and t-BuOK (0.84 mmol) in toluene (10 mL), and the mixture was stirred at r.t. until pyridazine 1 was consumed (TLC). 10% aq NaOH (50 mL) and CH2Cl2 (30 mL) were added to the mixture with stirring. The organic layer was separated, washed with H2O (50 mL), dried (MgSO4), and concentrated under reduced pressure. The residue was transferred to an open-bed column of silica gel (2.5 × 4 cm), which was eluted with hexane–EtOAc (3:1) to give the symmetric carbonates 2, or the asymmetric carbonates 4 or 6, and then eluted with EtOAc to isolate 4,5-dichloropyridazin-3(2H)-one quantitatively for reuse. Phenyl 2-Phenylethyl Carbonate (4) White solid; yield: 148 mg (87%); mp 83–85 °C. IR (KBr): 3109, 3081, 3058, 3033, 2969, 2938, 2895, 2868, 1753, 1492, 1260, 1210, 1077, 967, 778, 753, 699, 499 cm–1. 1H NMR (300 MHz, CDCl3): δ = 3.00 (t, J = 7.0 Hz, 2 H), 4.38–4.43 (m, 2 H), 7.10–7.35 (m, 10 H). 13C NMR (75 MHz, CDCl3): δ = 35.1, 69.1, 121.0, 121.2, 126.1, 126.4, 126.9, 128.7, 129.1, 129.6, 129.7, 137.1, 151.1, 151.2, 153.7. HRMS (EI): m/z [M+] calcd for C15H14O3: 242.0943; found: 242.0941.