2-enoylpyridine N-oxides Research Articles

Enantioselective Construction of Pyridine N-Oxides Featuring 2,3-Dihydrofuran Motifs via Phosphine-Catalyzed [4 + 1]-Annulation of 2-Enoylpyridine N-Oxides with Morita-Baylis-Hillman Carbonates.

The first example of phosphine-catalyzed enantioselective [4 + 1] annulations between 2-enoylpyridine N-oxides and Morita-Baylis-Hillman carbonates is described. When 1,2-bis[(2 R,5 R)-2,5-dimethylphospholano]benzene monoxide is employed as organocatalyst, Morita-Baylis-Hillman carbonates react with 2-enoylpyridine N-oxides smoothly to afford a series of optically active 2,3-dihydrofurans in high yields (up to 96%) with excellent stereoselectivities (96 → 99% ee and >20:1 dr). Importantly, the method offers a facile synthetic approach to enantioenriched pyridine N-oxides featuring 2,3-dihydrofuran motifs.

ChemInform Abstract: Asymmetric Direct Vinylogous Michael Addition to 2‐Enoylpyridine N‐Oxides Catalyzed by Bifunctional Thio‐Urea.

Catalytic enantioselective direct vinylogous Michael addition of α,α-dicyanoalkenes to 2-enoylpyridine N-oxides with a bifunctional organocatalyst is described. The methodology offers an efficient way to install an asymmetric carbon–carbon bond at the γ-position of α,α-dicyanoalkenes in excellent regio-, diastereo-, and enantioselectivity. Further, application in desymmetrization of achiral α,α-dicyanoalkene to access highly functionalized enantioenriched cyclohexylidenemalononitrile derivatives has been demonstrated.

N-Heterocyclic carbene-catalyzed diastereoselective synthesis of β-lactone-fused cyclopentanes using homoenolate annulation reaction.

NHC-catalyzed annulation of enals with 2-enoylpyridines or 2-enoylpyridine N-oxides leading to the diastereoselective synthesis of β-lactone-fused cyclopentanes is reported. The reaction proceeds via the generation of homoenolate equivalent intermediates and tolerates a broad range of functional groups.

Asymmetric direct vinylogous Michael addition to 2-enoylpyridine N-oxides catalyzed by bifunctional thio-urea.

Catalytic enantioselective direct vinylogous Michael addition of α,α-dicyanoalkenes to 2-enoylpyridine N-oxides with a bifunctional organocatalyst is described. The methodology offers an efficient way to install an asymmetric carbon-carbon bond at the γ-position of α,α-dicyanoalkenes in excellent regio-, diastereo-, and enantioselectivity. Further, application in desymmetrization of achiral α,α-dicyanoalkene to access highly functionalized enantioenriched cyclohexylidenemalononitrile derivatives has been demonstrated.

ChemInform Abstract: Enantioselective Mukaiyama—Michael with 2‐Enoyl Pyridine N‐Oxides Catalyzed by PYBOX‐DIPH‐Zn(II)‐Complexes at Ambient Temperature.

A chiral PYBOX-DIPH-Zn(II) catalyzed enantioselective Mukaiyama–Michael reaction of acyclic silyl enol ethers with 2-enoylpyridine N-oxides has been studied in external additive free conditions at ambient temperature. The methodology offers straightforward access to a variety of functionalized chiral 1,5-dicarbonyl compounds, which could easily be elaborated into synthetically viable pyrones via hydrolysis followed by cyclization. A transition state model has been proposed to explain the stereochemical outcome.

2-Enoylpyridine N-Oxides in Asymmetric Mukaiyama-Michael Additions

Key words Mukaiyama–Michael reaction - copper catalysis - bisoxazoline ligands

Enantioselective Mukaiyama–Michael with 2-enoyl pyridine N-oxides catalyzed by PYBOX-DIPH-Zn(ii)-complexes at ambient temperature

A chiral PYBOX-DIPH-Zn(II) catalyzed enantioselective Mukaiyama-Michael reaction of acyclic silyl enol ethers with 2-enoylpyridine N-oxides has been studied in external additive free conditions at ambient temperature. The methodology offers straightforward access to a variety of functionalized chiral 1,5-dicarbonyl compounds, which could easily be elaborated into synthetically viable pyrones via hydrolysis followed by cyclization. A transition state model has been proposed to explain the stereochemical outcome.

Enantioselective synthesis of 3,4-dihydropyran derivatives via a Michael addition reaction catalysed by chiral pybox–diph–Zn(ii) complex

An enantioselective Michael addition of cyclic 1,3-dicarbonyls to 2-enoylpyridine N-oxides catalyzed by a chiral pybox-diph-Zn(II) complex has been developed. The corresponding Michael adducts have been obtained in high yields with up to >99% ee. The Michael adduct has been transformed to biologically active 2,4-disubstituted hexahydroquinoline. A plausible transition-state model has been proposed to explain the stereochemical outcome of the reaction.

Enantioselective Michael Addition of Malonates to 2-Enoylpyridine N-Oxides Catalyzed by Chiral Bisoxazoline–Zn(II) Complex

An enantioselective Michael addition of malonates to 2-enoylpyridine N-oxides catalyzed by a chiral bisoxazoline-Zn(II) complex has been developed. The corresponding Michael adducts have been obtained in high yields with up to 96% ee. A plausible transition-state model has been proposed to explain the stereochemical outcome of the reaction.

Zn(II) Complexes Catalyzed Asymmetric Friedel-Crafts Alkylation of Pyrroles

In this paper, the authors developed a very efficient catalyst for the enantioselective Friedel-Crafts alkylation of pyrroles with 2-enoylpyridine N-oxides. The alkylation products are obtained in high yields and high enantioselectivities. Electron-rich furan and benzene derivatives also undergo this Friedel-Crafts reaction with high yield and enantioselectivity.

Enantioselective Friedel−Crafts Alkylation of Pyrroles Catalyzed by PYBOX-DIPH-Zn(II) Complexes

A highly enantioselective Friedel-Crafts alkylation of pyrroles with 2-enoylpyridine N-oxides catalyzed by chiral PYBOX-DIPH-Zn(II) complexes has been developed. The catalyst offers substantial substrate scope and furnished alkylated pyrroles in excellent yields (up to 99%) and enantioselectivities (up to >99% ee).