6. Multi-component reactions involving additions to alkenes

Carbonyl compounds and imines are preferred reaction partners for isonitriles in Passerini and Ugi reactions. Activated multiple C-C bonds can also undergo nucleophilic attack by isonitriles to initiate multicomponent sequences.

Addition of an isonitrile to an α,β-unsaturated ketone or ester can lead to iminofurans via Michael addition of the isonitrile, followed by cyclization of the enolate onto the nitrilium intermediate. Formally, this is again a [4+1] cycloaddition. These reactions on the simplest carbonyl derivatives are not observed without the use of Lewis acids such as gallium chloride (figure 69 ) [128].