Lewis Base Catalyzed [4+2] Annulation of Electron‐Deficient Chromone‐Derived Heterodienes and Acetylenes

Abstract

Lewis base catalyzed [4+2] annulation reactions between electron-deficient chromone oxa- and azadienes and acetylene carboxylates provide tricyclic benzopyrones inspired by natural products. An asymmetric synthesis of the tricyclic benzopyrones was developed by using modified cinchona alkaloids as enantiodifferentiating Lewis base catalysts.

A One‐pot Facile Construction of 1H‐1,2,3‐Triazolyl 1,2‐Dihydropyridyl Derivatives and Evaluation of Bioactivity Profile

“…Further, authors also reported phenylhydrazones, pyrazole carboxylates and pyrazolyl methanones as biologically active compounds . While research elsewhere reported the synthesis of dihydropyridines, pyrano pyridopyrimidinones, benzopyranopyridinones and tricyclic benzopyrones by the chemical transformation of 3‐formylchromones with the retention of the chromone ring . Similar trend has been observed in synthesis of 2‐hydroxybenzoylpyridones and pyridines by the ring opening of 3‐formylchromone …”

Cascade Syntheses Routes to the Centrocountins

“…This rearrangement, by analogy, proceeds through pyrylium cations 20 , similar to the transformation of 11 into 12 . In addition, we observed that the N ‐tosyl analogue 22 did not rearrange because the push–pull effect is lacking in this acid‐stable dihydropyridine (Scheme c) 8a…”

Alkynes in Organocatalysis

“…Achiral phosphines such as PPh 3 and PBu 3 can be used for the synthesis of tricyclic benzopyrones 38 through a formal [4+2] annulation reaction depicted in Scheme 21. [39] The phosphine catalyst, according to the aforementioned mechanism, transforms electron-poor acetylenes into nucleophilic zwitterions, which can react in a 1,4-addition to 3-formylchromones 37 to give a stabilized oxanion. This species further undergoes a 1,4-addition to the resulting activated alkenes to liberate the catalyst and deliver the cycloaddition adduct 38.…”