(S)-2,15-Cl2-DHTP–boron complex
catalyst for the asymmetric Diels–Alder cycloaddition of 2′-hydroxychalcones
and dienes was developed and tested. The resulting cyclohexenes with
three chiral centers were obtained in high yields (up to 98%) with
excellent stereoselectivities (up to >20:1 endo/exo, >99% ee). This catalytic system features
high efficiency,
broad substrate scopes, and mild reaction conditions. In addition,
a DFT study was performed to explain the stereochemical course of
the asymmetric induction.
The synthesis and
application of a newly designed C
2-symmetric
chiral-substituted 1,16-dihedroxytetraphenylene
(DHTP) is reported. Efficient syntheses of enantiopure substituted
DHTP were accomplished, and these enantiopure compounds were used
as organocatalysts in asymmetric allylboration of ketones under very
mild conditions. Accordingly, several tertiary alcohols were generated
in moderate to good yields with up to 99% ee by using the catalyst
(S)-2,15-Br2-DHTP. A gram-scale reaction
was achieved in 99% yield with 96% ee.
(S)-2,15-Br2-DHTP-catalyzed asymmetric
conjugate addition of boronic acids to β-trifluoromethyl α,β-unsaturated
ketones and enones was studied. The reaction afforded the corresponding
Michael addition products in moderate to high yields with excellent
enantioselectivities (up to 99:1 er). This catalytic system features
mild reaction conditions, high efficiency, and tolerance to heteroarylboronic
acids.
An efficient catalytic asymmetric Darzens reaction of N-protected isatins with diazoacetamides using a chiral BINOL/Ti(OPr) complex as the catalyst has been developed. This reaction is a straightforward method for the synthesis of spiro-epoxyoxindoles in 40-95% yields, up to >20:1 dr and up to >99% ee. A gram-scale reaction was also achieved in 95% yield with excellent stereoselectivity and enantioselectivity (>20:1 dr, >99% ee).
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