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Wang et al. Chem Synth 2023;3:12 https://dx.doi.org/10.20517/cs.2023.01 Page 15 of 20

Figure 19. Chiral phosphoric acid-catalyzed C-H insertion reactions of α-carbonyl sulfoxonium ylides to indoles. This figure is used with
permission from the American Chemical Society [79] .

Figure 20. Organocatalytic asymmetric tandem cyclopropanation/hemiaminalization reaction of 2’-hydroxycinnamaldehydes and
stabilized α-carbonyl sulfoxonium ylides. This figure is used with permission from the American Chemical Society [80] .

In addition, the synthetic applications of the protocol were also demonstrated by the versatile
derivatizations of the cyclopropane-fused chromane 74 and the cyclopropanation product 73. As shown in
Figure 21, the hemiacetal functionality of 74 can be leveraged as a synthetic handle enabling access to some
other compounds. A treatment of 74 with PCC gives rise to the oxidization of the hemiacetal group to form
compound 81 in moderate yield. 4 could be smoothly reduced to 82 in 67% yield by using triethylsilane in
the presence of BF •OEt, and could also be converted to 83 in 91% yield with NaBH . Moreover,
3
4
cyclopropanation product 73 could undergo intramolecular asymmetric oxa-Michael reaction. With
Cinchona alkaloid-derived bifunctional catalysts C18 and C19 for the Michael addition, the tricyclic ring-
fused products trans-84 and cis-84 could be obtained in moderate yield with high diastereoselectivity and
excellent enantioselectivity, respectively.

In 2022, Leveille et al. discovered that the benzopyrylium triflates 88 in situ generated from chromenones/
quinolones 85 and triisopropylsilyl triflate (TIPSOTf) could react with sulfoxonium ylides 50 via a
cyclopropylation process to access a range of cyclopropanated products 86 in 18%-90% yield .
[81]
Furthermore, the authors also converted several products 86 into benzo[b]oxepines 87 with 57%-90% yield
via acid-mediated ring-expansion in the presence of a nucleophile [Figure 22] . In addition, the authors
[81]