The invention relates to a method for adding a compound (A) to an H-functional starting compound (BH) in the presence of a catalyst, wherein the at least one compound (A) is selected from at least one group consisting of alkylene oxide (A-1), lactone (A-2), lactide (A-3), cyclic acetal (A-4), lactam (A-5), cyclic anhydride (A-6) and oxygen-containing heterocyclic compound (A-7) different from (A-1), (A-2), (A-3), (A-4) and (A-6), wherein the catalyst comprises an organic, n-protic Brønsted acid (C), wherein n≥2 and is an element of the natural numbers and the degree of protolysis D is 0