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Page 14 of 20 Wang et al. Chem Synth 2023;3:12 https://dx.doi.org/10.20517/cs.2023.01

Figure 17. Organocatalytic formal N-H insertion reaction of arylamines with α-keto sulfoxonium ylides bearing two aryl groups. This
[77]
figure is used with permission from the Royal Society of Chemistry .

Figure 18. Chiral squaramide-catalyzed enantioselective H-N insertion of α-carbonyl sulfoxonium ylides. This figure is used with
3
permission from the Royal Society of Chemistry [78] .

in moderate-to-good yields with very good stereocontrol. Moreover, after a Wittig olefination to the
chromanol moiety of 70, the tricyclic ring-fused compounds 74 could be further transformed into a series of
[80]
cyclopropanation products 73 [Figure 20] .

In the proposed reaction pathway [Figure 20], acid mediated condensation of 2’-hydroxycinnamaldehydes
72 and chiral catalyst C17 forms reactive iminium ion intermediate 75, which is attacked by the
sulfoxonium ylides 50 via transition state 76 to furnish intermediate 77. And then, an intramolecular
nucleophilic substitution reaction of 77 leads to the formation of iminium ion 78, which would undergo
hydrolysis to release the catalyst C17 and to deliver 2,3-trans cyclopropane 79. Subsequent epimerization of
the α-position to the aldehyde function would give rise to the generation of 2,3-cis-isomers 80, which
undergo hemiacetalization to give cyclopropane-fused chromane products 74.