Techniques for tight pitch patterning are provided. In one aspect, a patterning method includes: forming mandrels on a substrate; forming spacers that are undoped alongside the mandrels, wherein gaps are present between the spacers; filling the gaps with a sacrificial material having a dopant; forming a mask having an opening marking a cut region of at least one of the spacers; removing the sacrificial material from the cut region of the at least one spacer via the mask; removing the mask; performing an anneal to diffuse the dopant from the sacrificial material into the spacers to form doped spacers, wherein following the anneal the cut region of the at least one spacer remains undoped; removing the cut region of the at least one spacer selective to the doped spacers; and patterning features in the substrate using the doped spacers as a hardmask. A patterning structure is also provided.