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Synlett 2018; 29(02): 189-192
DOI: 10.1055/s-0036-1591311
DOI: 10.1055/s-0036-1591311
letter
Efficient Method to Synthesize Benzhydrazides by In Situ Oxidation/Coupling of Benzylic Alcohols with Azodicarboxylates
Further Information
Publication History
Received: 11 July 2017
Accepted after revision: 29 August 2017
Publication Date:
16 October 2017 (online)
Abstract
An efficient synthesis of benzhydrazides has been achieved through the direct acylation of azodicarboxylates with benzylic alcohols in moderate to high yields. The method represents the first practical approach to amides containing a hydrazine structural unit from benzylic alcohols.
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References and Notes
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Dialkyl 1-Aroylhydrazine-1,2-dicarboxylates; General Procedure
The appropriate dialkyl azodicarboxylate (1.5 mmol) was added to a stirred mixture of CuO nanoparticles (10 mol%) and a benzylic alcohol (0.75 mmol) in MeCN (0.5 mL) under argon. A 30% solution of t-BuOOH (2 equiv) was added dropwise, and the mixture was stirred at 80 °C for 6 h. When the benzaldehyde generated in situ had been consumed (TLC; decolorization of the azodicarboxylate was also observed), the mixture was treated with NaBH4 (0.5 mmol, 20 mg) in MeOH (0.5 mL). After 5 min, the reaction was quenched with aq NH4Cl (1 mL) and brine (1 mL). The cooled mixture was centrifuged to separate the catalyst then extracted with EtOAc (2 × 20 mL). The extracts were dried (MgSO4), filtered, and concentrated in vacuo to give a crude product that was purified by column chromatography [silica gel, EtOAc–hexanes (1:4)]. Diisopropyl 1-Benzoylhydrazine-1,2-dicarboxylate White solid; yield: 85%; mp 123 °C. 1H NMR (500 MHz, CDCl3): δ = 7.7 (m, 2 H), 7.52 (t, J = 7.4 Hz, 1 H), 7.4–7.45 (m, 2 H), 7.26 (br s, 1 H), 4.98–5.05 (m, 1 H), 4.8–4.9 (m, 1 H), 1.29 (d, J = 6.0 Hz, 6 H), 1.08 (d, J = 5.4 Hz, 6 H). Diethyl 1-Benzoylhydrazine-1,2-dicarboxylate Colorless oil; yield: 80%. 1H NMR (500 MHz, CDCl3): δ = 7.68 (d, J = 7.2 Hz, 2 H), 7.30–7.50 (m, 3 H), 7.24 (br s, 1 H), 4.23 (q, J = 7.2 Hz, 2 H), 4.15 (q, J = 7.2 Hz, 2 H), 1.29 (t, J = 7.2 Hz, 3 H), 1.07 (t, J = 7.2 Hz, 3 H).