نتایج جستجو برای: stereoselectively
تعداد نتایج: 274 فیلتر نتایج به سال:
(-)-Spicigerolide was stereoselectively synthesized from a protected (S)-lactaldehyde. The synthesis of the polyacetylated framework relied on two Zn-mediated stereoselective additions of alkynes to aldehydes as well as a regiocontrolled [3,3]-sigmatropic rearrangement of an allylic acetate. The pyranone moiety was constructed via ring-closing metathesis.
We employ vortex grinding to generate a [2.2]paracyclophane in the organic solid state. The vortex grinding is aided with the addition of a small amount of liquid phase to facilitate topochemical [2 + 2] photodimerizations that generate the cyclophane stereoselectively and in up to quantitative yield. The use of the liquid phase increases the scope of the vortex method.
The title compound, C(6)H(9)NO(4), was prepared stereoselectively as a precursor for 1-aza-dienes in a study of hetero-Diels-Alder reactions. The configuration of the C=N double bond was found to be Z, corroborating earlier assignments of similar compounds based only on NMR and IR spectroscopic analysis.
The reaction of dienyl carbamates with PhI(OR)2 in the presence of rhodium catalysts affords vinyl aziridines which are in situ regio- and stereoselectively opened to afford oxyamination products resulting from a selective S(N)2 (Rh2(OAc)4/PhI(OPiv)2) or S(N)2' (Rh2(OPiv)4/PhI(OAc)2) opening. The scope and limitations of this tandem process are described.
Three types of small ring compounds (epoxides, aziridines and cyclopropanes) can be synthesized stereoselectively via ylide route. Among them, the stereochemistry of vinyloxiranes, vinylaziridines, cyclopropylesters, amides and ketones can be tuned by the choice of reaction conditions and ylides with varying heteroatoms and ligands. Optically active epoxides and acetylenylaziridines can be prep...
A rapid and simple procedure was devised for the synthesis of multifunctionalized cyclic β-amino esters and γ-amino alcohols via the 1,3-dipolar cycloaddition of nitrile oxides to β-aminocyclopentenecarboxylates. The opening of the isoxazoline reductive ring to the corresponding highly functionalized 2-aminocyclopentanecarboxylates occurred stereoselectively with good yields.
Vinyl-substituted (Z)-stilbenes are stereoselectively synthesised on treatment of 4-arylbuta-2,3-dien-1-ols with arylboronic acids in the presence of a rhodium(i) catalyst. The reaction proceeds through the regioselective addition of organorhodium(i) species across the aryl-substituted carbon-carbon double bond of the allene moiety and subsequent delta-elimination of Rh(i)-OH.
We describe hydrogen-bonded dimers of catechol that act collectively as a single template to direct an intermolecular [2+2] photocycloaddition in the solid state. The directed reactivity involves discrete, six-component hydrogen-bonded assemblies and a photoreaction that occurs stereoselectively and in quantitative yield.
Cascading to alkaloids: an 18-step total synthesis of (-)-dendrobine is based on a reaction cascade with a key amine group. The amine is the initiator of the cascade and provides an efficient method for installing the stereocenters at C11 and C3. The overall transformation occurs stereoselectively only when the conversion is carried out without the isolation of intermediates.
C(2)-symmetric bisamidines 8 have been tested as chiral Brønsted bases in the Diels-Alder reaction of anthrones and N-substituted maleimides. High yields of cycloadducts and significant asymmetric inductions up to 76% ee are accessible. The proposed mechanism involves proton transfer between anthrone and bisamidine, association of the resulting ions and finally a cycloaddition step stereoselect...
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