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He et al. Chem Synth 2023;3:35 https://dx.doi.org/10.20517/cs.2023.14 Page 3 of 9
Figure 1. Representative natural products and bioactive compounds containing the indole-2-yl-pyrans skeleton.
Scheme 1. Profile of the construction of NHC-catalyzed construction of dihydropyranone.
(entry 2, 72% yield, 35% ee). Various inorganic bases could be used in this transformation (entries 4-5), and
NaHCO was found as the most efficient one that could give 3a with good yield and excellent
3
enantioselectivity (entry 5, 75% yield, 94% ee). Screening different reaction solvents did not show further
improvements in either yields or enantioselectivities (entries 6-7). When 5 Å MS was used as the additive,
the yield and the enantioselectivity increased slightly higher (entry 8, 78% yield, 97% ee). Further
