Isopropenyl Esters (iPEs) in Green Organic Synthesis

The need for greener compounds able to replace conventional ones with similar reactivity is crucial for the development of sustainable chemistry. Isopropenyl esters (iPEs) represent one eco-friendly alternative to acyl halides and anhydrides. This review provides a comprehensive overview of the preparation methodologies and reported synthetic applications of iPEs and, in particular, of isopropenyl acetate (iPAc). Intriguingly, the presence of a C=C double bond adjacent to the ester functionality makes iPEs appealing in different chemoselective organic synthesis transformations. For instance, the acyl moiety is suitable for transesterification reactions in presence of different heteroatom-based nucleophiles (C-, O-, N-, S-, Se-); these reactions are irreversible thanks to the formation of acetone, obtained upon keto-enol tautomerization of the prop-1-en-2-ol (isopropenyl) leaving group. Similarly, the unsaturation contained in the isopropenyl synthon could be selectively exploited in organic synthesis for electrophilic and/or radical additions as well as in metal-catalyzed cross-coupling reactions. To conclude, iPEs recently found major interest in the direct modification of biomass (i.e. lignin or cellulose) and in the implementation of tandem reactions of esterification-acetalization by exploiting the co-formation of acetone during the reaction.