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A Convenient Preparation of Di-p-chlorobenzyl Azodicarboxylate (DCAD) for Mitsunobu Couplings
12 December 2008 (online)
Gram-scale synthesis of pure, bench-stable solid di-p-chlorobenzyl azodicarboxylate (DCAD) is performed in two steps without resorting to chromatography. This novel reagent effects Mitsunobu couplings with yields comparable to DEAD or DIAD, while addressing several of the drawbacks frequently associated with these common reagents.
Mitsunobu reaction - azo compounds - alcohols - esters - DCAD
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Our originally reported R f for the hydrazine dicarboxylate 4 is misleading, as the material was impure due to the presence of residual imidazole.
Optimum results were achieved using CDI and CBA obtained from Alfa Aesar.5
Imidazole is water soluble while 4 is not. Use of 1:1 hexanes-Et2O leads to substantial loss of product 4. Exposure time of the product to solvent can be minimized by using vacuum filtration.