Commonly, isocyanides are synthesized by dehydration of formamides. The formamide can be dehydrated with toluenesulfonyl chloride, phosphorus oxychloride, phosgene, diphosgene, or the Burgess reagent in the presence of a base such as pyridine or triethylamine.
The formamide precursors are, in turn, prepared from amines by formylation with formic acid or formyl acetyl anhydride.or from the Ritter reaction of alkenes (and other sources of carbocations) and hydrogen cyanide.