A Novel Approach to N′,N′-Diarylhydrazides from N′-Arylhydrazides

Abstract

A novel method for conversion of N′-arylhydrazides to N′,N′-diarylhydrazides via aerobic oxidation has been achieved. The aerobic reaction was performed using CuCl₂ as a catalyst in NH₃·H₂O–MeOH to give good yields under mild conditions. The mechanism of the reaction is also discussed.

Key words

N′-arylhydrazides - N′,N′-diarylhydrazides - aerobic oxidation - CuCl₂ - geminal - N′,N′-diarylhydrazines

• References and Notes

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• 13 General Procedure for the Preparation of Products 2a–m A mixture of 1 (1 mmol) and CuCl₂ (10 mol%) in 25% NH₃·H₂O (3 mL) and MeOH (15 mL) was stirred at r.t. for 0.5 h in O₂ atmosphere (balloon). When the reaction was completed (as monitored by TLC; EtOAc–PE = 1:4 as eluent). The solvent was evaporated under reduced pressure. The resulting mixture was extracted with CH₂Cl₂ (15 mL) and washed with sat. brine (15 mL) three times. The combined organic layers were dried over anhydrous MgSO₄. Then the organic solvent was evaporated. The residue was purified by column chromatography (EtOAc–PE = 1:4 as eluent) to give the desired product 2.
• 14 Procedure for the Preparation of Product 2a on Multigram Scale To a mixture of MeOH (250 mL) and 25% NH₃·H₂O (50 mL), 1a (100 mmol) and CuCl₂ (10 mmol) were added successively in O₂ atmosphere (balloon). The mixture was stirred for 3 h at r.t. The solvent was concentrated under reduced pressure. The resulting mixture was poured into H₂O (200 mL). The slurry mixture was filtered through Buchner funnel and washed thoroughly with H₂O to remove the cupric salts. The white crystals were collected and dried to give the product 2a (9.26 g, yield 81.9%).