The synthesis of pyrimidine‐spirofused indolines from 1,3,5‐triazinanes with 2‐sulfonyliminoindolines has been achieved under catalyst‐ and additive‐free conditions, in which five atoms of 1,3,5‐triazinanes were introduced to the spiro‐annulation products via a (5+1) pathway. Subsequently, this strategy was extended to 3‐aminoindoles and 3‐aminobenzothiophenes, but a different reaction pathway (3+3) was observed. In these cases, three‐atoms of 1,3,5‐triazinanes were incorporated into pyrimidine‐fused indoles/benzothiophenes. These two transformations demonstrate the potential and versatility of 1,3,5‐triazinanes to construct nitrogen‐heterocycles.