Organic synthesis
Catalytic Mitsunobu chemistry with recyclable azo reagents
Open access · cc by · source: Europe PMC
Ethyl arylazocarboxylates plus iron phthalocyanine and air replace stoichiometric DEAD in Mitsunobu esterifications with high inversion.
Key findings
Catalyst 1a (3,4-dichlorophenyl) is best for carboxylic acids and stereochemical inversion; 1j (4-cyanophenyl) is best for other nucleophiles. Toluene at RT gave 88% yield with perfect inversion; flame-activated 5 Å sieves gave 94% yield. Air is the sacrificial oxidant.
Methodology
Authors screened ethyl 2-arylhydrazinecarboxylates as catalytic azo sources, reoxidized hydrazines with O2 and iron phthalocyanine, optimized solvent, molecular sieves, and concentration, and measured yield/inversion on secondary alcohols and other nucleophiles.
Limitations
Plant-scale process metrics (E-factor on multi-kilo batches) are not provided; some chlorinated solvents still erode inversion, and PPh3 remains stoichiometric.
How this study connects
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Ethyl arylazocarboxylates plus iron phthalocyanine and air replace stoichiometric DEAD in Mitsunobu esterifications with high inversion.
Evidence for the claim as stated.
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