We report the first example of dearomative (3 + 2) cycloadditions of 3-nitro(aza)-indole, -benzofuran, and -benzothiophene derivatives in the presence of allenyl sulfones, using sulfinate ammonium ion pairs as organocatalytic promoters. The methodology provides a new, facile, and efficient protocol for the synthesis of functionalized 2,3-fused cyclopentannulated indolines and dihydrobenzofurans.