Diastereoselective synthesis of PEGylated imidazolidines, oxazolidines, thiazolidines, pyrrolo[3,4-c]pyrroles and fulleropyrrolidines in high yields is reported. The 1,3-dipolar cycloaddition of azomethine ylides generated via thermal ring-opening of PEGylated aziridines to ketenimines, ketenes, thioketones, maleimides, DMAD and fullerene C₆₀ was found to proceed under different conditions. The use of C[dbnd]O, C[dbnd]N and C[dbnd]S dipolarophiles requires more harsh reaction conditions, compared with C[dbnd]C and C[tbnd]C dipolarophiles, to suppress the side reaction of aziridine “dimerization”. The stereocontrol of the product configuration is achieved through stereospecificity of two consecutive concerted reactions: electrocyclic aziridine ring opening followed by 1,3-dipolar cycloaddition of the resulting azomethine ylide: only trans-adducts are formed from cis-aziridines, whereas trans-aziridines give exclusively cis-adducts. The structure and molecular-mass distribution of the resulting PEGylated heterocycles are exhaustively characterized by ¹H, ¹³C NMR, IR and HRMS.