10 research outputs found
Highly Enantioselective Synthesis of 3,4-Dihydropyrans through a Phosphine-Catalyzed [4+2] Annulation of Allenones and β,γ-Unsaturated α‑Keto Esters
A phosphine-catalyzed novel [4+2]
annulation process was devised
employing allene ketones as C<sub>2</sub> synthons and β,γ-unsaturated
α-keto esters as C<sub>4</sub> synthons. In the presence of
an l-threonine-derived bifunctional phosphine, 3,4-dihydroÂpyrans
were obtained in high yields and with virtually perfect enantioÂselectivities.
The synthetic value of the dihydroÂpyran motif was demonstrated
by a concise preparation of an anti-hyperÂcholesterolÂemic
agent
Bifuctional Amino-Squaramides Catalyzed Asymmetric Spiroannulation Cascades with Aliphatic β,γ-Unsaturated α-Keto Esters: Controlling an Aldehyde Enolate
A quinidine-derived squaramide <b>Ib</b> catalyzed
cyclization
reaction of β-oxo aldehydes <b>1</b> and aliphatic or
aromatic β,γ-unsaturated α-keto ester <b>2</b> is described. Using cyclic aldehyde substrates, this procedure provided
a promising approach to a variety of spiro-3,4-dihydropyrans bearing
three continuous quaternary and tertiary stereocenters in moderate
to good yield with high stereoselectivities. Substituents on the nitrogen
atoms of the squaramide moiety of the catalyst proved crucial to the
reaction outcome. The stereochemistry of the three newly formed chiral
centers (<i>trans</i>-selective) of the major product indicates
a Micheal addition/hemiacetalization domino sequence for the present
annulations
Phosphine-Catalyzed Enantioselective [4 + 2] Annulation of <i>o</i>‑Quinone Methides with Allene Ketones
A phosphine-catalyzed
highly enantioselective [4 + 2] annulation
between <i>ortho</i>-quinone methides and allene ketones
has been developed. The reported method led to the formation of chromane
derivatives in high yields and excellent enantioselectivity. This
is the first time that <i>ortho</i>-quinone methides are
employed in phosphine-mediated cyclization reactions
Chiral Spirooxindole–Butenolide Synthesis through Asymmetric N‑Heterocyclic Carbene-Catalyzed Formal (3 + 2) Annulation of 3‑Bromoenals and Isatins
By
using an N-heterocyclic carbene catalyst bearing a hydroxyl
moiety, the asymmetric formal (3 + 2) cyclization of aryl 3-bromoenals
and isatins was achieved to produce a series of chiral spirooxindole–butenolides
including an alkenyl-substituted compound, which underwent benzannulations
with benzynes to form intriguing spirocyclic scaffolds
NHC-Catalyzed <i>O</i>‑Selective Addition of Nitrosoarenes with Aldehydes
An NHC-catalyzed <i>O</i>-selective addition of nitrosoarenes with aldehydes probably upon a dual-activation mode was developed, generating a variety of <i>O</i>-acyl hydroxylamines without any detectable competing amidation byproducts
Three-Component Assembly of Conjugated Enyne Scaffolds via <i>E</i>-Selective Olefination of Ynals
Benefited by the accessible ynamido–lithium intermediates <b>Ib</b> from a Cu-catalyzed azide–alkyne cycloaddition in the presence of stoichiometric amounts of LiOH, a mild and flexible three-component route to conjugated enyne scaffolds was successfully achieved via a formal <i>E</i>-selective olefination strategy
Divergent NHC-Catalyzed Oxidative Transformations of 3‑Bromoenal: Selective Synthesis of 2<i>H</i>‑Pyran-2-ones and Chiral Dihydropyranones
A selective synthesis of either 2<i>H</i>-pyran-2-ones (<b>4</b>) or chiral dihydropyranones
(<b>6</b>) from the same substrates of 3-bromoenals and 1,3-dicarbonyl
compounds upon oxidative <i>N</i>-heterocyclic carbene catalysis
is presented. It is shown that the oxidative transformation of 3-bromoenals
under NHC catalyst can be well controlled to proceed through two pathways,
i.e., elimination of reducible β-bromide or by an external oxidant <b>3</b>, allowing the selective generation two sorts of unsaturated
acyl azoliums, respectively
Enantioselective [4 + 2]-Annulation of Oxadienes and Allenones Catalyzed by an Amino Acid Derived Phosphine: Synthesis of Functionalized Dihydropyrans
An
enantioselective [4 + 2]-annulation process between cyano-activated
oxadienes and allenones is developed. An l-valine-derived
phosphine was efficient in catalyzing the reaction, and a wide range
of highly functionalized dihydropyrans were prepared in high yields
and with excellent enantioselectivities
A Facile Approach for the Asymmetric Synthesis of Oxindoles with a 3‑Sulfenyl-Substituted Quaternary Stereocenter
With the employment of a threonine-incorporating multifunctional catalyst <b>9</b>, Michael addition of 3-sulfenyloxindoles to nitroolefins proceeded stereoselectively, leading to the formation of oxindoles with a 3-sulfenyl-substituted quaternary center in excellent yields, and with high diastereoselectivities and excellent enantioselectivities
Construction of Enantioenriched Quaternary C–Cl Oxindoles through Palladium-Catalyzed Asymmetric Allylic Substitution with Chloroenolates
A palladium-catalyzed asymmetric
chloroenolate allylation with
vinyl benzoxazinanones under mild reaction conditions has been developed,
affording a series of optically active 3,3-disubstituted oxindoles
exhibiting a chloro-group and a linear aryl amino side chain in good
yields with up to 96% ee. Versatile functional group tolerance on
the benzene ring has been demonstrated, and the utility of this method
was probed by a scale-up synthesis and highlighted by product derivatizations