“…Kumar et al [26] developed a proline-catalyzed Mannich reaction-cyclization sequence of succinaldehyde and an in situ-generated arylimine, in which the succinaldehyde contributes three carbon atoms to the pyrrole ring. α,β-Unsaturated aldehydes have also been used as the C 3 donor to construct pyrrole scaffolds [27,28]; (ii) [1 + 4] annulation, in which (hetero)arylamines are reacted with a C 4 donor to form the pyrrole ring; many functional molecules, such as bioderived furans [29], (Z)-enynols [30], 1-vinylpropargyl alcohols [31], doubly activated cyclopropanes [32], and enynals [33], can be used as C 4 counter reagents. The carbon-based 1,4-biselectrophiles, such as the 1,4-dicarbonyl compounds [34,35], γ-car-bonyl tert-butyl peroxides [36], and dihydrofurans [37] have also been reported to construct the pyrrole skeletons through this type of annulation; and (iii) [1 + 2 + 2] annulation, in which (hetero)arylamines are reacted with two different molecules, and each of them contributes two carbon atoms to construct a pyrrole ring [38][39][40][41][42].…”