Page 55 - Read Online
P. 55
Yang et al. Chem Synth 2023;3:7 https://dx.doi.org/10.20517/cs.2022.38 Page 19 of 54
Scheme 22. N-heterocyclic carbene-catalyzed annulation of benzolactone-2-ones 43 and enals 44. This figure is used with permission
from the Royal Society of Chemistry [71] .
Scheme 23. Organocatalyzed aldol/cyclization reaction of α-keto lactone 43 with α-isothiocyanato imide 46. This figure is used with
permission from the American Chemical Society [72] .
In 2010, a rosin-derived thiourea catalyst C9 catalyzed asymmetric aldol/cyclization cascade reaction of
isothiocyanato butyrolactone 48 as C-N-C synthon with isatins 49 was reported by Jiang et al. . It is
[72]
proposed that, with the dual activation of rosin-based thiourea C9, this strategy allowed rapid construction
of highly functional bispiro[thiooxazoline/thiocarbamate-butyrolactone-oxindole]s 50 and 51 with
moderate diastereoselectivities (70:30-92:8 dr). However, the author did not provide their specific ees
[Scheme 25].
