Catalyst component for the polymerization of olefins comprising Mg, Ti and an electron donor of formula (I) Where R1 and R2, independently, are selected from hydrogen and C1-C15 hydrocarbon groups, optionally contain an heteroatom selected from halogen, P, S, N, O and Si, which can be fused together to form one or more closed cycles and A is a bivalent bridging group.