The Michael addition-alkylation process proceeded smoothly to provide 2,3-dihydrofurans as trans-diastereomers in moderate to good isolated yields (33–92%) and excellent enantioselectivities (29–>99% ee).
A sulfa-Michael/aldol/lactonization
cascade reaction has been established
to construct isotetronic acid-fused thiochromanes in a highly stereoselective
fashion (≥11:1 dr, 35–98% ee). The tricyclic products
were obtained in 35–99% isolated yields in the presence of
a bifunctional squaramide. Three reactive sites of β,γ-unsaturated
α-ketoester, including the less-explored ester carbonyl group,
were sequentially utilized to construct two fused heterocycles in
a one-pot operation.
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