Decarboxylative Annulation of α-Amino Acids with γ-Nitroaldehydes

Cu(II)-Catalyzed Decarboxylative (4 + 2) Annulation of Coumarin-3-Carboxylic Acids with In Situ Generated α,β-Unsaturated Carbonyl Compounds from tert-Propargylic Alcohols

Cu(II)-catalyzed decarboxylative oxidative (4 + 2) annulation of coumarin-3-carboxylic acids with tert-propargylic alcohols, via the in situ generated α,β-unsaturated carbonyl compounds by the Meyer-Schuster rearrangement, has been developed. This protocol involving indirect C-H functionalization offers access to diverse naphthochromenone architectures with good to excellent yields.

Inverse hydride shuttle catalysis enables the stereoselective one-step synthesis of complex frameworks

The rapid assembly of complex scaffolds in a single step from simple precursors identifies as an ideal reaction in terms of efficiency and sustainability. Indeed, the direct single-step synthesis of complex alkaloid frameworks remains an unresolved problem at the heart of organic chemistry in spite of the tremendous progress of the discipline. Herein, we present a broad strategy in which dynamically assembled ternary complexes are converted into valuable azabicyclic scaffolds based on the concept of inverse hydride shuttle catalysis. The ternary complexes are readily constructed in situ from three simple precursors and enable a highly modular installation of various substitution patterns. Upon subjection to a unique dual-catalytic system, the transient intermediates undergo an unusual hydride shuttle process that is initiated by a hydride donation event. Furthermore, we show that, in combination with asymmetric organocatalysis, the product alkaloid frameworks are obtained in excellent optical purity.

Synthesis of bridgehead-azacycles via dual C-N/C-C annulation of α-amino acids, aminals and maleimides

The synthesis of various bridged azacyclic adducts has recently become a reemerging topic due to their bioactive and natural product mimic profiles. Accordingly, herein, we report a method for easy access to succinamide-bridged azacyclic derivatives through the metal-free polarization-controlled dual C-N/C-C annulation of readily available α-amino acids, 2-amino benzaldehydes or pyrrole/indole-2-aldehyde and maleimide substrates. This cascade features a rare dipolarophile-induced diastereo-selective amidative annulation, followed by 3 + 2 cycloaddition as key steps.

Chichibabin pyridinium synthesis via oxidative decarboxylation of photoexcited α-enamine acids

A visible light-induced decarboxylative Chichibabin pyridinium synthesis between α-amino acids and aldehydes was developed. When the in situ generated α-enamine acids were photoexcited, they were oxidized by aerobic oxygen to give radical cation species. After decarboxylation and further oxidation, the generated iminium undergoes Chichibabin cyclization to afford pyridiniums. This photochemical protocol enables the synthesis of various tetra-substituted pyridiniums and related natural products in one-step.

One-pot three-component reaction of p-quinone monoacetals, l-proline and naphthols to afford N-aryl-2-arylpyrrolidines

A one-pot three-component reaction of p-quinone monoacetals (or p-quinol ethers), l-proline and naphthols is developed for the synthesis of N-aryl-2-arylpyrrolidines under mild conditions with high chemo- and regioselectivity.

A three-component, general and practical route for diastereoselective synthesis of aza-spirocyclic pyrazolones via a decarboxylative annulation process

An efficient, general, and practical route for highly diastereoselective synthesis of aza-spirocyclic pyrazolones from easily available α-amino acids, aldehydes, and alkylidene pyrazolones by means of a decarboxylative annulation process is reported.

Traceless Redox-Annulations of Alicyclic Amines

Amines such as 1,2,3,4-tetrahydroisoquinoline undergo redox-neutral annulations with ortho-(nitromethyl)benzaldehyde. Benzoic acid acts as a promoter in these reactions, which involve concurrent amine α-C-H bond and N-H bond functionalization. Subsequent removal of the nitro group provides access to tetrahydroprotoberberines not accessible via typical redox-annulations. Also reported are decarboxylative annulations of ortho-(nitromethyl)benzaldehyde with proline and pipecolic acid.

Redox-Annulations of Cyclic Amines with ortho-Cyanomethylbenzaldehydes

Amines such as 1,2,3,4-tetrahydroisoquinoline undergo redox-neutral annulations with ortho-cyanomethylbenzaldehydes. These amine α-C-H bond functionalization reactions are promoted by acetic acid. The resulting β-aminonitriles can be converted to the corresponding β-aminoalcohols in diastereoselective fashion.

One-pot cascade synthesis of azabicycles via the nitro-Mannich reaction and N-alkylation

A one-pot, metal-free process for the synthesis of azabicycles is developed. The key transformations involved a cascade of double intramolecular cyclizations via the nitro-Mannich reaction and N-alkylation, providing various ring systems of azabicycles in yields up to 81% and an isomeric ratio of 62 : 1. This approach offers considerable advantages in terms of the handling of small molecules, the flexibility to introduce a functionalized side chain, and gives direct access to various azabicycles.

Regio- and Enantioselective (Het)arylation of β-Alkenyl Pyrroline to α-Aryl-β-alkenyl Pyrrolidines

Regio- and enantioselective direct arylation of β-alkenyl pyrroline is reported. A wide range of electron-rich arenes and heteroarenes reacted under mild conditions with different β-alkenyl pyrrolines to provide structurally diverse α-aryl-β-alkenyl pyrrolidines with very good yields and excellent regioselectivity. Enantioselective reaction in the presence of Lewis acids and chiral phosphoric acids provided the desired arylated product with 73% enantiomeric excess.

Redox-Annulations of Cyclic Amines with 2-(2-Oxoethyl)malonates

Amines such as 1,2,3,4-tetrahydroisoquinoline undergo redox-neutral annulations with 2-(2-oxoethyl)malonates in the presence of catalytic amounts of benzoic acid. These reactions install a fully saturated five-membered ring and provide access to structures closely related to the natural products crispine A and harmicine.

Transition-Metal-Free Access to Pyridocarbazoles from 2-Alkynylindole-3-carbaldehydes via Azomethine Ylide

An efficient approach for the synthesis of functionalized tetrahydro-pyrido/quinolinocarbazoles from 2-alkynylindole-3-carbaldehydes and l-proline utilizing a metal-free decarboxylative cyclization, ring expansion, and ring contraction strategy via the generation of azomethine ylide was developed. The reaction of 2-alkynylindole-3-carbaldehydes with l-thioproline leads to the formation of γ-carbolines. By virtue of this expedient method, a diverse range of biologically active heteroannulated carbazoles can be synthesized efficiently.

Decarboxylative Annulation of α-Amino Acids with β-Ketoaldehydes

Indolizidine and quinolizidine derivatives are readily assembled from l-proline or (±)-pipecolic acid and β-ketoaldehydes via a decarboxylative annulation process. These reactions are promoted by acetic acid and involve azomethine ylides as reactive intermediates.

The synthesis of imidazo[1,5-a]quinolinesviaa decarboxylative cyclization under metal-free conditions

An iodine-mediated decarboxylative cyclization was developed from α-amino acids and 2-methyl quinolines under metal-free conditions, affording a variety of imidazo[1,5-a]quinolines with moderate to good yields.

An iodine-mediated decarboxylative cyclization was developed from α-amino acids and 2-methyl quinolines under metal-free conditions, affording a variety of imidazo[1,5-a]quinolines with moderate to good yields.

Acetic Acid Promoted Redox Annulations with Dual C-H Functionalization

Amines such as 1,2,3,4-tetrahydroisoquinoline undergo redox-neutral annulations with 2-alkylquinoline-3-carbaldehydes as well as the corresponding 4-alkyl isomers and pyridine analogues. These processes involve dual C-H bond functionalization. Acetic acid is used as a cosolvent and acts as the sole promoter of these transformations.

The direct decarboxylative allylation of N-arylglycine derivatives by photoredox catalysis

The direct decarboxylative allylation of N-arylglycine derivatives has been accomplished via visible-light photoredox catalysis.