Synthesis of Allylic Amide Functionalized 2H-Chromenes and Coumarins Using a One-Pot Overman Rearrangement and Gold(I)-Catalyzed Hydroarylation

Microwave-Assisted Copper(II)-Catalyzed Cascade Cyclization of 2-Propargylamino/Oxy-Arylaldehydes and O-Phenylenediamines: Access to Densely Functionalized Benzo[f]Imidazo[1,2-d][1,4]Oxazepines and Benzo[f]Imidazo[1,2-d][1,4]Diazepines

A highly efficient microwave-assisted copper(II)-catalyzed cyclization cascade was established starting from readily accessible O/N-propargylated 2-hydroxy or 2-aminobenzaldehydes and o-phenylenediamines to synthesize densely functionalized imidazo[1,2-d][1,4]oxazepines and imidazo[1,2-d][1,4]diazepines in high yields (up to 93%). This one-pot two-step process was found to be highly atom economical (-H₂O, -H₂) and operationally simple and enabled the generation of two new heterocycle rings (seven- and five-membered) and three new C-N bonds in a single synthetic operation. These reactions well tolerated a variety of substituents including electron-donating and electron-withdrawing groups and furnished the desired fused heterocycles in high yields under microwave irradiation in a very short reaction time. The mechanism of the established protocol involves sequential imine formation-intramolecular cyclization-air oxidation followed by 7-exo-dig cyclization steps. A comparative study between the microwave-assisted approach and conventional heating was also performed to demonstrate the advantages of the microwave-assisted protocol in terms of high yield and shorter reaction time.

Gold-Catalyzed Hydroarylation Reactions: A Comprehensive Overview

The hydroarylation of alkynes, alkene, and, allene is a cost-effective and efficient way to incorporate unsaturated moieties into aromatic substrates. This review focuses on gold-catalyzed hydroarylation, which produces aromatic alkenes,...

Synthesis of 2H-chromenes: recent advances and perspectives

As one type of chromene, 2H-chromenes represent important oxygen heterocycles, which not only widely exist in natural products, pharmaceutical agents and biologically relevant molecules, but have also been used broadly in materials science and organic synthesis. Two major synthetic strategies have been developed towards such compounds. This review mainly focuses on the recent advances in this field, including benzopyran ring formation involving cyclization reactions and the late-stage functionalization of the parent 2H-chromenes.

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

β-Hydroxyalkylphosphine sulfides undergo [1,3]- or [1,4]-sulfur atom phosphorus-to-carbon migration in the presence of Lewis or Brønsted acids. The direction of sulfur atom migration depends on the type of acid used for the reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some control experiments and DFT calculations.

Catalyst-Free Synthesis of α-Functionalized 2H-Chromenes in Water: A Tandem Self-Promoted pseudo-Substitution and Decarboxylation Process

A catalyst-free decarboxylative reaction between β-keto acids and 2H-chromene acetals in water was developed. This reaction featured a broad substrate scope and easily obtainable starting materials to afford α-functionalized 2H-chromenes in high yields. The synthetic value of this protocol was also demonstrated by the scale-up synthesis and versatile conversions of the title product into other useful compounds. In addition, control experiments indicated that water was essential for the reactivity. Mechanistic studies further revealed that the reaction proceeded through a self-promoted tandem pseudo-substitution and decarboxylation process.

A cascade Claisen rearrangement/o-quinone methide formation/electrocyclization approach to 2H-chromenes

A new approach to 8-substituted 2H-chromenes is developed, featuring a novel cascade aromatic Claisen rearrangement/o-quinone methide formation/6π-electrocyclization.