21 research outputs found
Formal Asymmetric α‑Alkenylation of Aldehydes and the Synthetic Application toward Forming α-<i>exo</i>-Methylene-γ-butyrolactones and Skipped Dienes
A formal asymmetric
α-alkenylation of aldehydes is reported
based on the organocatalytic reaction of aldehydes with nitroacrylates.
The reaction proceeds in a one-pot manner forming the products with
up to 77% yield and up to >99% ee. This strategy is also successfully
applied for the synthesis of α-<i>exo</i>-methylene-γ-butyrolactones
and skipped diene scaffolds in a highly enantioselective manner
1,4-Naphthoquinones in H‑Bond-Directed Trienamine-Mediated Strategies
The synthesis of optically active, carboannulated dihydronaphthoquinone and naphthoquinone derivatives with up to four stereogenic centers is demonstrated by H-bond-directed, trienamine-mediated [4 + 2]-cycloadditions. The outcome of the reaction between 2,4-dienals and 1,4-naphthoquinones is controlled by the substituent in the 2-position of the 1,4-naphthoquinone. In the case of sterically demanding 2-substituted derivatives, dihydronaphthoquinones are obtained. However, when a hydrogen atom is present in the 2-position, a subsequent oxidation of the initially formed cycloadducts occurs yielding naphthoquinones
Asymmetric [3 + 2] Cycloaddition of Vinylcyclopropanes and α,β-Unsaturated Aldehydes by Synergistic Palladium and Organocatalysis
The
stereoselective [3 + 2] cycloaddition between vinylcyclopropanes
and α,β-unsaturated aldehydes promoted by combined palladium
and organocatalysis is disclosed. The unique synergistic catalytic
system allows for the stereoselective formation of highly substituted
cyclopentanes with up to four stereocenters in high yields and selectivities.
Vinylcyclopropanes with two different geminal substituents facilitate
the formation of cyclopentanes containing a quaternary stereocenter.
Furthermore, the developed reaction performs well on gram scale, and
a number of transformations are demonstrated
Étienne-Hyacinthe de Ratte and Pierre Marie Auguste Broussonet, Montpellier, [France], to James Edward Smith, 12 Great Marlborough Street, London
De Ratte, secretary of the Académie des Sciences of Montpellier, informs Smith he has been elected a Correspondent Member. Broussonet has appended his own communication
Asymmetric [3 + 2] Cycloaddition of Vinylcyclopropanes and α,β-Unsaturated Aldehydes by Synergistic Palladium and Organocatalysis
The
stereoselective [3 + 2] cycloaddition between vinylcyclopropanes
and α,β-unsaturated aldehydes promoted by combined palladium
and organocatalysis is disclosed. The unique synergistic catalytic
system allows for the stereoselective formation of highly substituted
cyclopentanes with up to four stereocenters in high yields and selectivities.
Vinylcyclopropanes with two different geminal substituents facilitate
the formation of cyclopentanes containing a quaternary stereocenter.
Furthermore, the developed reaction performs well on gram scale, and
a number of transformations are demonstrated
Catalytic Asymmetric Synthesis of 4‑Nitropyrazolidines: An Access to Optically Active 1,2,3-Triamines
The
first catalytic enantio- and diastereoselective synthesis of 4-nitropyrazolidines
is presented. Asymmetric hydrogen-bonding activation of nitro-olefins
facilitated the 1,3-dipolar cycloaddition with hydrazones, affording
optically active 4-nitropyrazolidines containing three continuous
stereogenic centers as a single diastereomer in up to 99% ee. Furthermore,
it is demonstrated that the optically active 4-nitropyrazolidines
can be applied as precursors for the synthesis of highly interesting
1,2,3-triamines
Controlling Asymmetric Remote and Cascade 1,3-Dipolar Cycloaddition Reactions by Organocatalysis
The regio- and stereoselective control
of cycloaddition reactions
to polyconjugated systems has been demonstrated by applying asymmetric
organocatalysis. Reaction of 2,4-dienals with nitrones allows for
a highly regio- and stereoselective 1,3-dipolar cycloaddition in the
presence of an aminocatalyst. The first cycloaddition on the remote
olefin can be followed either by a cascade reaction or by other selective
reactions of the remaining olefin. The chiral products are obtained
in good to high yields and excellent diastereo- and enantioselectivities.
The remote selective concept has been extended to 2,4,6-trienals by
means of a novel enantioselective triple cascade 1,3-dipolar cycloaddition
reaction. The formation of chiral poly 1,3-amino alcohols is also
demonstrated
Beyond Classical Reactivity Patterns: Shifting from 1,4- to 1,6-Additions in Regio- and Enantioselective Organocatalyzed Vinylogous Reactions of Olefinic Lactones with Enals and 2,4-Dienals
Organocatalysis
is shown to expand the classical reactivity pattern
for conjugate addition reactions. It is demonstrated that the site
selectivity can be extended from 1,4- to 1,6-additions for the enantioselective
vinylogous additions of methyl-substituted vinylogous lactones to
enals and 2,4-dienals. This novel reactivity is demonstrated for methyl-substituted
olefinic azlactones and butyrolactones. Their synthetic potential
is first highlighted by the development of the organocatalytic regioselective
vinylogous 1,4-addition to enals which proceeds with a very high level
of double-bond geometry control and excellent enantioselectivity.
The concept is developed further for the unprecedented intermolecular
enantioselective organocatalyzed vinylogous 1,6-addition to linear
2,4-dienals, by which the site selectivity of the process is extended
from the β-position to the remote δ-position of the 2,4-dienal.
The organocatalyst controls the newly generated stereocenter six bonds
away from the stereocenter of the catalyst with a high level of enantiocontrol,
and the products are obtained with full control of double-bonds configuration.
The scope of these new reaction concepts is demonstrated for a series
of aliphatic and aryl-substituted enals and 2,4-dienals undergoing
enantioselective vinylogous reactions with methyl-substituted olefinic
azlactones and butyrolactones. Furthermore, mechanistic considerations
are presented which can account for the change from 1,4- to 1,6-selectivity.
Finally, a number of different transformations of the optically active
1,4- and 1,6-addition products are demonstrated
Beyond Classical Reactivity Patterns: Shifting from 1,4- to 1,6-Additions in Regio- and Enantioselective Organocatalyzed Vinylogous Reactions of Olefinic Lactones with Enals and 2,4-Dienals
Organocatalysis
is shown to expand the classical reactivity pattern
for conjugate addition reactions. It is demonstrated that the site
selectivity can be extended from 1,4- to 1,6-additions for the enantioselective
vinylogous additions of methyl-substituted vinylogous lactones to
enals and 2,4-dienals. This novel reactivity is demonstrated for methyl-substituted
olefinic azlactones and butyrolactones. Their synthetic potential
is first highlighted by the development of the organocatalytic regioselective
vinylogous 1,4-addition to enals which proceeds with a very high level
of double-bond geometry control and excellent enantioselectivity.
The concept is developed further for the unprecedented intermolecular
enantioselective organocatalyzed vinylogous 1,6-addition to linear
2,4-dienals, by which the site selectivity of the process is extended
from the β-position to the remote δ-position of the 2,4-dienal.
The organocatalyst controls the newly generated stereocenter six bonds
away from the stereocenter of the catalyst with a high level of enantiocontrol,
and the products are obtained with full control of double-bonds configuration.
The scope of these new reaction concepts is demonstrated for a series
of aliphatic and aryl-substituted enals and 2,4-dienals undergoing
enantioselective vinylogous reactions with methyl-substituted olefinic
azlactones and butyrolactones. Furthermore, mechanistic considerations
are presented which can account for the change from 1,4- to 1,6-selectivity.
Finally, a number of different transformations of the optically active
1,4- and 1,6-addition products are demonstrated
A New Organocatalytic Concept for Asymmetric α‑Alkylation of Aldehydes
The organocatalytic asymmetric α-alkylation
of aldehydes
by 1,6-conjugated addition of enamines to <i>p</i>-quinone
methides is described. Employing a newly developed class of chiral
secondary amine catalysts, α-diarylmethine-substituted aldehydes
with two contiguous stereocenters have been synthesized in a simple
manner with good diastereocontrol and excellent enantioselectivity