Chemoselective Transformations of Amides: An Approach to Quinolones from β-Amido Ynones

Brønsted acid-catalyzed two-component tandem condensation and cycloisomerization to 6(2H)-isoquinolinones

An attractive Brønsted acid-catalyzed two-component reaction of 2-alkynyl-4-hydroxybenzaldehydes 1 and primary amines 2 to various 6(2H)-isoquinolinones 3 has been developed. This catalytic system realized an efficient tandem condensation and cycloisomerization reaction to 6(2H)-isoquinolinones 3 in good to excellent yields via a one-pot synthesis, in which two different kinds of C-N bonds were constructed in a straightforward manner. Remarkably, the reaction tolerated various aliphatic, aryl-substituted amines, including chiral amino alcohols and amino acids. The practicality of this approach rendered it a viable alternative for the construction of various 6(2H)-isoquinolinones.

Acid-Promoted Phosphorylation of Ynones for the Synthesis of Phosphoryl Enones

An efficient phospha-aldol/Meyer-Schuster rearrangement cascade reaction between propargylic aldehydes and phosphine oxides has been developed in which various phosphoryl enones were obtained in moderate to excellent yields. A comprehensive series of mechanistic experiments, including the identification of key intermediates and the application of 18O isotope labeling, has confirmed that this cascade reaction proceeds through a phospha-aldol followed by Meyer-Schuster rearrangement cascade reaction.

Using Quinolin-4-Ones as Convenient Common Precursors for a Metal-Free Total Synthesis of Both Dubamine and Graveoline Alkaloids and Diverse Structural Analogues

The Rutaceae family is one of the most studied plant families due to the large number of alkaloids isolated from them with outstanding biological properties, among them the quinoline-based alkaloids Graveoline 1 and Dubamine 2. The most common methods for the synthesis of alkaloids 1 and 2 and their derivatives involves cycloaddition reactions or metal-catalyzed coupling processes but with some limitations in scope and functionalization of the quinoline moiety. As a continuation of our current studies on the synthesis and chemical transformation of 2-aminochalcones, we are reporting here an efficient metal-free approach for the total synthesis of alkaloids 1 and 2 along with their analogues with structural diversity, through a two-step sequence involving intramolecular cyclization, oxidation/aromatization, N-methylation and oxidative C-C bond processes, starting from dihydroquinolin-4-ones as common precursors for the construction of the structures of both classes of alkaloids.

Brønsted Acid-Catalyzed Intramolecular Tandem Double Cyclization of γ-Hydroxy Acetylenic Ketones with Alkynes into Naphtho[1,2-b]furan-3-ones

A metal-free and atom-economic route for the synthesis of naphtho[1,2-b]furan-3-ones has been realized via p-TsOH·H2O-catalyzed intramolecular tandem double cyclization of γ-hydroxy acetylenic ketones with alkynes in formic acid. The benzene-linked furanonyl-ynes are the key intermediates obtained by the scission/recombination of C-O double bonds. Further, the structural modifications of the representative product were implemented by reduction, demethylation, substitution, and [5 + 2]-cycloaddition.