An environmentally benign cascade reaction of chromone-3-carboxaldehydes with ethyl 2-(pyridine-2-yl)acetate derivatives for highly site-selective synthesis of quinolizines and quinolizinium salts in water

Abstract

A novel protocol for the synthesis of quinolizines (3) and quinolizinium salts (4) from chromone-3-acrboxaldehydes 1 with ethyl 2-(pyridine-2-yl)acetate derivatives 2 via an unprecedented cascade reaction in water was constructed....

Metal-catalyzed reactions of organic nitriles and boronic acids to access diverse functionality

“…First, the reaction proceeds with the formation of an arylnickel intermediate (A) via transmetalation of arylboronic acids and Ni(II)catalysts. Thereafter, coordination of (A) to nitrile provides In the same year (2019), a similar method was developed by Shao and Chen's group for the synthesis of 2-arylquinolines (87) via a Pd(II)-catalyzed tandem reaction of 2-aminostyryl nitriles (86) with arylboronic acids (Scheme 42). 65 The mechanistic experiment reveals a nucleophilic addition of arylpalladium to the nitrile group followed by an intramolecular cyclization and dehydration to give the desired product.…”

“…85h,i In this regard, in 2020, a Pd(II)-catalyzed C-C activation-initiated reaction of 2-(3-phenyloxiran-2-yl)benzonitriles (124) with arylboronic acids has been developed by Chen and Shao's group for the synthesis of benzo-fused dipyrromethene derivatives (125) (Scheme 62). 86 The transformation involves the cleavage and reconstruction of multiple chemical bonds via β-carbon elimination for the synthesis of benzo-fused dipyrromethenes. Arylboronic acids with bulky substituents provide better yields as compared with less bulky substituents, suggesting a positive steric influence on the reaction.…”

Efficient Synthesis of 7H‐Chromeno[3,2‐c]quinolin‐5‐ium Salts and Quinolin‐4‐ones through Acid‐Promoted Cascade Reaction of 3‐Formylchromones and Anilines

“…In our previous study, we described an effective strategy for the synthesis of a series of bicyclic imidazopyridinium derivatives by the reaction of 3‐formylchromones with N ‐benzyl nitro ketene aminals under reflux in ethanol (Scheme 1a) [58] . In 2020, Yan reported a novel protocol for the synthesis of quinolizinium salts from 3‐formylchromones with ethyl 2‐(pyridine‐2‐yl)acetate derivatives under acidic conditions (Scheme 1b) [59] . In these reactions, the 3‐formylchromones undergo ring‐opening reaction at the same time when the new imidazopyridinium and quinolizinium salts are formed.…”

Synthesis of 5H-Chromeno[2,3-d]pyrimidin-5-one Derivatives via Microwave-Promoted Multicomponent Reaction

“…Chroman-4-one as a privileged motif widely exists in natural products and bioactive molecules. Thus, chroman-4-one-based substrates (e.g., 3-formylchromone) were often used as versatile modules to generate diversified natural product-like scaffolds. − 3-Formylchromone can undergo not only a series of annulation reactions − but also various ring-opening reactions − owing to its structural characteristics. Continuing our ongoing interest in N-heterocycles, − we designed a new MCR including 3-formylchromones, amines, and formaldehyde to construct 1,3-oxazinane-fused chroman-4-ones (path b in Scheme ).…”

“…According to the literature, − ,− possible mechanisms for the formation of 3a and 3a′ were proposed as shown in Scheme . First, p -toluidine attacks the β-position of the highly reactive α,β-unsaturated ketone system in 3-formylchromone 1a followed by a ring-opening reaction, delivering the key intermediate B .…”