“…The electrophilic character of these structures also allows cycloaddition reactions, particularly those with nucleophilic olefins, to take place under very mild conditions. Such reactions have provided routes to a variety of novel heterocyclic structures which have proved to be very useful targets, not only due to their eventual biological and pharmacological properties, but especially to their wide and versatile use as synthetic intermediates or useful building blocks for the synthesis of amino acids, pyrroles, proline, indoles, pyrazines, and aza-sugars derivatives, amongst many other compounds [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ].…”