In several lectures in 1960 Rolf Huisgen introduced the concept of 1,3-dipolar cycloadditions providing five-membered heterocycles; the first reports were published shortly afterwards.1 In analogy to the Diels–Alder reaction, a 1,3-dipole reacts as a 4π system with the general formula “abc” with a dipolarophile “d=e” or “d≡e” (delivering 2π electrons) in a (3+2) cycloaddition to give the five-membered product (Scheme 1). The 1,3-dipoles “abc” cannot be described by neutral octet formulas, but they bear a positive charge at the center atom “b”; the two sextet formulas with neutral “b” explain the choice of the name 1,3-dipole for these compounds.2 The four formulas depicted in Scheme 1 reflect the ambivalent character of 1,3-dipoles with nucleophilic and electrophilic properties; possible diradical mesomeric formulas are not shown in this illustration. These heteroallyl or heteropropargyl anion systems react with a variety of double- and triple-bond systems to provide five-membered cycloadducts with neutralization of the formal charges.