The title of this post comes from a comment posted by Ryan, who asks about isocyanide’s role (in the form of the anion of tosyl isocyanide, or TosMIC) in two named reactions, Van Leusen and Ugi FCR. “In Van Leusen, it (the isocyanide) acts as an electrophile: however, in Ugi, it acts as a nucleophile”. Here are some valence bond forms for this species;