Azolides acid halide synthesis

Staab introduced azolides as versatile reagents in organic synthesis. The reaction of carbonyldiimid-azolide with carboxylic acids produces imidazolides under mild conditions which can be converted by the action of hydrogen halides to acid halides in high yield (equation 20). The method does not even require the isolation of the imidazolides, but can be carried out as a one-pot synthesis. The possibility of carrying out this reaction at low temperatures allows the preparation of temperature sensitive compounds. Formyl chloride, which decomposes at -40 °C, has been prepared in this way. 

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