Ethyl 3-(3,4-Dichlorophenyl)carbazate

Taniguchi (Kanazawa Univ.) et al. have reported a new catalytic Mitsunobu reaction with ethyl 3-(3,4-dichlorophenyl)carbazate [E0998] (10 mol%) under atmospheric oxidation conditions. They describe the catalytic system in which ethyl 2-arylazocarboxylate, an oxidized azo form of E0998, plays a role as diethyl azodicarboxylate (DEAD). The azo compound-promoted Mitsunobu reactions of alcohols with carboxylic acids in the presence of triphenylphosphine successfully proceed to give ester products. Then, generated E0998 is reoxidized to its azo form by in situ iron catalyzed atmospheric oxidation. E0998 is suitable for the reactions with carboxylic acids. On the other hand, E1299 provides good results with nucleophiles other than carboxylic acids.

Typical procedure¹⁾: A mixture of ethyl L-(-)-lactate (118 mg, 1 mmol), 4-nitrobenzoic acid (184 mg, 1.1 mmol), triphenylphosphine (525 mg, 2.0 mmol), ethyl 3-(3,4-dichlorophenyl)carbazate (24.9 mg, 1 mmol), iron(II) phthalocyanine (56.8 mg, 0.1 mmol) and activated MS5Å (500 mg) in toluene (250 µL) is irradiated for ca. 1 minute in an ultrasound bath and vigorously stirred at room temperature for 12 h under air (balloon). After the reaction mixture is filtered, the solvent is removed under reduced pressure. The residue is purified by silica gel chromatography (eluent: n-hexane/EtOAc = 6:1) to give (R)-1-ethoxycarbonylethyl 4-nitrobenzoate (249 mg, 0.93 mmol, 93%, 99:1 e.r.) as a white solid.