Acetylenes and nitriles as unconventional reactants for aza-Wittig reactions

The classic version of aza-Wittig reactions, namely, reactions between phosphazenes and compounds with polar double bonds, is widely employed in organic synthesis to produce C=N bonds. However, only a limited number of aza-Wittig reactions between phosphazenes and compounds with triple bonds is known, which has a lot to do with certain structural features of the reactants, wherein additional activation is required. This review provides a guide to those rare examples of aza-Wittig reactions with acetylenes and nitriles. A unique trait of these atom-economic processes is that they afford Wittig or new aza-Wittig reagents, respectively, which offers new opportunities for employing these reactions in organic syntheses, especially those of N-heterocyclic compounds.