3 research outputs found
Enantioselective Synthesis of <i>anti</i>–<i>syn</i>-Trihalides and <i>anti</i>–<i>syn</i>–<i>anti</i>-Tetrahalides via Asymmetric β‑Elimination
Structural motifs containing contiguous
halide-bearing stereocenters are common in natural products as well
as bioactive molecules. A few successful examples have been reported
in the area of asymmetric vicinal dihalogenation of alkenes for accessing
dihalogenated products; in this report, an alternative generation
method of contiguous halide-bearing stereocenters α,β,γ,δ
relative to carbonyl group in excellent enantioselectivity is proposed
by utilizing a Song’s oligoEG catalyst-catalyzed asymmetric β-elimination.
According to this methodology, a wide range of <i>anti</i>–<i>syn</i>-trihalides and <i>anti</i>–<i>syn</i>–<i>anti</i>-tetrahalides
with high levels of enantioselectivity were synthesized. The synthetic
utility of the contiguous halide-bearing stereocenters was demonstrated
by several transformations. The results of high-resolution mass spectrometry
indicated that the favorable interaction between catalyst and one
of the enantiomers of racemic contiguously multihalogenated ketone
contributed to the original enantioselectivity of dehydrohalogenation.
A deuterium kinetic isotope effect experiment revealed that this β-elimination
reaction proceeds by the <i>E</i>2 mechanism. This strategy
opens a new pathway for the asymmetric synthesis of contiguous halide-bearing
stereocenters of great complexity
Asymmetric Synthesis of Trisubstituted Tetrahydrothiophenes via in Situ Generated Chiral Fluoride-Catalyzed Cascade Sulfa-Michael/Aldol Reaction of 1,4-Dithiane-2,5-diol and α,β-Unsaturated Ketones
A chiral fluoride-catalyzed
asymmetric cascade sulfa-Michael/aldol
condensation reaction of 1,4-dithiane-2,5-diol and a series of α,β-unsaturated
ketones is described to access chiral trisubstituted tetrahydrothiophene
derivatives. The target products, including the spiro tetrahydrothiophene
derivatives bearing a five-, six-, and seven-membered ring, were highly
functionalized and showed high ee value. This established protocol
realized a highly enantioselective reaction with a catalytic amount
of KF and Song’s chiral oligoEG via in situ generated chiral
fluoride to construct useful heterocyclic skeletons with great complexity
Enantioselective Synthesis of <i>anti</i>–<i>syn</i>-Trihalides and <i>anti</i>–<i>syn</i>–<i>anti</i>-Tetrahalides via Asymmetric β‑Elimination
Structural motifs containing contiguous
halide-bearing stereocenters are common in natural products as well
as bioactive molecules. A few successful examples have been reported
in the area of asymmetric vicinal dihalogenation of alkenes for accessing
dihalogenated products; in this report, an alternative generation
method of contiguous halide-bearing stereocenters α,β,γ,δ
relative to carbonyl group in excellent enantioselectivity is proposed
by utilizing a Song’s oligoEG catalyst-catalyzed asymmetric β-elimination.
According to this methodology, a wide range of <i>anti</i>–<i>syn</i>-trihalides and <i>anti</i>–<i>syn</i>–<i>anti</i>-tetrahalides
with high levels of enantioselectivity were synthesized. The synthetic
utility of the contiguous halide-bearing stereocenters was demonstrated
by several transformations. The results of high-resolution mass spectrometry
indicated that the favorable interaction between catalyst and one
of the enantiomers of racemic contiguously multihalogenated ketone
contributed to the original enantioselectivity of dehydrohalogenation.
A deuterium kinetic isotope effect experiment revealed that this β-elimination
reaction proceeds by the <i>E</i>2 mechanism. This strategy
opens a new pathway for the asymmetric synthesis of contiguous halide-bearing
stereocenters of great complexity