Asymmetric Aza-Diels–Alder Reactions of in Situ Generated β,β-Disubstituted α,β-Unsaturated N–H Ketimines Catalyzed by Chiral Phosphoric Acids

Non-covalent organocatalyzed enantioselective cyclization reactions of α,β-unsaturated imines

Asymmetric cycloaddition is a straightforward strategy which enables the synthesis of structurally distinct cyclic derivatives which are difficult to access by other methodologies, using an efficient and atom-economical path from simple precursors. In recent years several asymmetric catalytic cyclization strategies have been accomplished for the construction of N-heterocycles using various catalytic systems such as chiral metal catalysts, chiral Lewis acids or chiral organocatalysts. This review presents an overview of the recent advances in enantioselective cyclization reactions of 1-azadienes catalyzed by non-covalent organocatalysts.

Base-Promoted One-Pot Four-Component Domino Strategy Involving Aldehydes and Ketones to Access Multifunctionalized Dihydropyridinones

The synthesis of multifunctionalized dihydropyridinones from aldehydes and ketones involves at least a three-step process, making route shortening a challenging task, especially in achieving a one-pot four-component synthesis via aldehydes and ketones precondensation. Herein, we discovered a [1 + 2 + 1 + 2] four-component domino cyclization reaction, a novel concept in 4CRs with commercially available ketones and aldehydes, which by initially combining aldehydes and ketones with Meldrum's acid and ammonium acetate (NH4OAc), respectively, they give dihydropyridones (>110 examples). This transformation features inexpensive additives and readily available starting materials, making it appropriate for rapid access to relevant pharmaceutical molecules containing dihydropyridinone-derived heterocycles. Also these compounds can be conveniently converted into trisubstituted and tetrasubstituted pyridines.

One-pot synthesis of functionalized dihydropyridin-2-ones via carbene-catalyzed base-controlled [3+3] annulation reaction

Herein, we have described a novel organocatalytic approach to access biologically important dihydropyridin-2-ones in a one-pot way with generally high yields (up to 99%) and excellent enantioselectivities (up to 99% ee). This reaction proceeded via a new dual activation mode, including in situ-generated α,β-unsaturated acylazoliums and 4-dimethylaminopyridinium salts that underwent a Michael addition/1,4-H migration/lactamization sequence. The base-triggered 4-dimethylaminopyridinium ylide formation pathway over the competing substitution reaction pathway of vicinal haloamines is noteworthy.

B(C6F5)3/Chiral Phosphoric Acid Catalyzed Asymmetric Aza-Diels-Alder Reaction of Imines and Unactivated Dienes

Herein, we report an asymmetric aza-Diels-Alder reaction of quinoxalinones or benzoxazinones with unactivated dienes by utilizing a B(C6F5)3/chiral phosphoric acid catalyst to construct chiral six-membered N-heterocycles. Various quinoxalinones or benzoxazinones with electron-withdrawing and electron-donating groups and unactivated dienes were tolerated (up to 99% yield and 99% ee) in the methodology with only 2 mol % catalyst loading. Moreover, the luminescence mechanism and photophysical properties of the product were tested and used for anticounterfeiting of QR codes.

Organocatalytic Asymmetric [4 + 2] Cyclization of Azadienes with Azlactones: Access to Chiral 3-Amino-δ-Lactams Derivatives

Herein, a series of chiral δ-lactam frameworks have been synthesized and catalyzed by chiral phosphoric acid (CPA) utilizing two kinds of open-chain aza-dienes and azlactones derived from amino acids. This powerful [4 + 2] annulation produces a broad substrate scope with functional group tolerance in yield up to 97% with up to 98:2 er. Moreover, a facile scale-up and straightforward conversion to diversely substituted products verify the synthetic utility of this method featuring good compatibility and high efficiency.

Highly diastereoselective synthesis of benzothiazolo[3,2-a]pyridines via [4 + 2] annulation reaction of 2-vinylbenzothiazoles and azlactones

An efficient AgOTf-catalyzed [4 + 2] annulation reaction of 2-vinylbenzothiazoles and azlactones was successfully performed under mild reaction conditions. With this approach, a series of novel benzothiazolo[3,2-a]pyridine derivatives was readily obtained in good to excellent yields (68-96%), with high diastereoselectivities and tolerating quite a broad scope of substituents. By using chiral phosphoric acid catalyst, the desired products were obtained in high enantioselectivities, up to -94%. This methodology provides a rapid and useful method for constructing fused benzothiazole derivatives.

An NHC-Catalyzed [3+2] Cyclization of β-Disubstituted Enals with Benzoyl Cyanides

The NHC-catalyzed asymmetric [3+2] cyclization of benzoyl cyanides to homoenolate generated in-situ from enals was reported. This methodology leads to the efficient construction of a series of chiral cyclic compounds...

A silver-catalyzed domino inverse electron-demand oxo-Diels-Alder reaction of 3-cyclopropylideneprop-2-en-1-ones with 2,3-dioxopyrrolidines via cyclobutane-fused furan

A silver-catalyzed diastereoselective one-pot domino cyclization-migration/inverse electron-demand oxo-Diels-Alder reaction has been disclosed in this communication through the in situ generated cyclobutane-fused furan intermediate with 4-vinyl-2,3-dioxopyrrolidine for the construction of 2-oxopyrrolidine-fused tricyclic compounds in moderate to good yields with a broad substrate scope under mild conditions. This new synthetic protocol features good efficiency and atom- and step-economy. A plausible reaction mechanism has also been proposed on the basis of previous reports, NMR tracing and control experiments.

Enamides and dienamides in phosphoric acid-catalysed enantioselective cycloadditions for the synthesis of chiral amines

This feature article describes how enamides and dienamides can participate in chiral phosphoric acid catalyzed enantioselective cycloadditions to prepare a wide range of cyclic amines.