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Wang et al. Chem Synth 2023;3:12 https://dx.doi.org/10.20517/cs.2023.01 Page 7 of 20

Figure 7. Chiral C -symmetric urea-catalyzed cyclopropanation of β,γ-unsaturated α-ketoesters. This figure is used with permission
2
[52]
from the American Chemical Society .

Figure 8. Chiral diamine-catalyzed asymmetric cyclopropanation of α,β-unsaturated ketones. This figure is used with permission from
the American Chemical Society [53] .

In 2008, Lu et al. reported an organocatalytic [4 + 1] cyclization reaction of nitroolefins 26 and sulfonium
ylides 1 under ortho-chlorophenyl thiourea C11 and N,N-dimethylaminopyridine (DMAP) cooperative
catalysis, allowing efficient and rapid access to diverse and structurally complex oxazolidin-2-ones (±)-27
[Figure 9] . In their proposed plausible mechanism, the thiourea catalyst enables formal (4 + 1)
[54]
cycloaddition to furnish isoxazoline N-oxide 29, which undergoes an intramolecular cyclization to form
intermediate 30. In the presence of DMAP, deprotonation from 30 releases intermediate 31, which could
convert into nitrene 33 via intermediate 32. Followed by Hofmann rearrangement and intramolecular
cyclization, the resulting intermediate 35 reacts with DMAP-H to deliver oxazolidin-2-one 27.
+

Impressively, the catalytic asymmetric version of the above [4 + 1] cyclization reaction between nitroolefins
26 and sulfonium ylides 1 was realized by the same group in 2012 [Figure 10] . The chiral C -symmetric
[55]
2
multiple hydrogen-bonding urea catalyst C9 shows the best positive effect on enantioselectivity and the
method displays a broad substrate scope to give optically active oxazolidin-2-ones 27 in good to excellent