Curtius rearrangement, electrophilic

Formation of mixed anhydrides also provides the basis for the synthesis of acyl azides (eq I ) and hence amines via the Curtius rearrangement. The azide ion is usually delivered to the most electrophilic carbonyl, but steric considerations may be important. The method is applicable even to strained cyclopropyl- and cyclobutylcarboxylic acids. Diisopropylethy-kunine (Hiinig s base) has been mooted as a superior base for the formation of mixed anhydrides. ... 

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