Unsubstituted or rimethyl substituted five-membered heterocycles react under thermal and high pressure conditions with activated ketones affording electrophilic substitution products (B). 2, 5_Dimethylfuran,-thiophene and pyrroles give substituted products (A). With dimethylpyrroles, B-substitution may occur leading to products (C). The reactions are supposed to proceed via ene-like reactions.