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Figure 9. ortho-chlorophenyl thiourea/DMAP cooperative catalysis for the [4 + 1] cyclization reaction of nitroolefins and stable
sulfonium ylides. This figure is used with permission from the American Chemical Society [54] .

Figure 10. Catalytic asymmetric [4 + 1] cyclization reaction of nitroolefins and stabilized sulfonium ylides. This figure is used with
permission from the Wiley-VCH Verlag [55] .

yields and stereoselectivities (65%-96% yields, > 95:5 dr, and 76%-94% ee). The authors think the formation
of chiral oxazolidin-2-ones depends largely on asymmetric [4 + 1] cyclization reaction, including a cascade
Michael addition/intramolecular O-alkylation/rearrangement process. In addition, stepwise operation at
temperature could ensure the high enantioselectivity of the reaction. Moreover, synthetic applications were
[57]
also conducted. (+)-epi-cytoxazone 39 and key intermediate 40 for synthesis of the valinoctin A 41 were
[56]
respectively provided after two steps.
Based on their successful implementation of thiourea/DMAP cooperative-catalysis strategy for the
diastereoselective [4 + 1] cyclization reaction of nitroolefins and sulfonium ylides , Xiao and coworkers
[54]
became interested in the application of the vital isoxazoline N-oxides 29 [Figure 9] intermediate as a type of
1,3-dipole species for the possible further reactions. In 2009, Lu et al. reported a catalyst-free sequential
intermolecular [4 + 1] and intramolecular [3 + 2] cycloaddition reaction between sulfonium ylides 1 and
alkene-tethered nitroolefins 42 [Figure 11] . The protocol exhibits a wide substrate scope and excellent
[58]