Synthesis of Heteroannulated Chromeno[2,3‐b]Pyridines: DBU Catalyzed Reactions of 2‐Amino‐6‐methylchromone‐3‐Carboxaldehyde with Some Heterocyclic Enols and Enamines

Abstract

Six new title pyridines are prepared by cyclocondensation of chromonealdehyde (I) with a variety of heterocyclic enols and enamines.

Utility of 6-Aminouracils for Building Substituted and Heteroannulated Pyrimidines: A Comprehensive Review

“…On the other hand, treatment of 6-aminouracil (1) with 2-amino-6-methylchromone-3-carboxaldehyde (114) in boiling DMF and DBU as catalyst gave 8-methyl-6H-chromeno [3',2':5,6]pyrido[2,3-d]pyrimidine-2,4(1H,3H),6-trione (115); through condensation of the aldehyde function with active methylene group followed by cyclocondensation with loss of NH3 molecule (Scheme 66). 99 Scheme 66 Moreover, 6-amino-5-thiocyanatopyrimidine-2,4-diones 152 were obtained, in good yields, by treating 6amino-1,3-disubstituted uracils 1 with ammonium thiocyanate (151) as thiocyanating agent in water, in the presence of H2O2, as oxidizing agent (Scheme 83). 118…”

Synthesis of Chromone-Related Pyrazole Compounds

“…Structurally diverse chromone-fused pyrazoles can be prepared by tandem reactions of 3-formylchromones with several pyrazole [ 51 ] and pyrazolone derivatives [ 52 ], including the cycloaddition reaction of 3-formylchromones with pyrazole- o -quinodimethane derivatives [ 53 ]. The treatment of 3-formylchromone 69 with 5-amino-3-methyl-1 H -pyrazole 70 in refluxing dimethylformamide/1,8-diazabicyclo[5.4.0]undec-7-ene (DMF/DBU) resulted in 3,7-dimethylchromeno[2,3- b ]pyrazolo[4,3- e ]pyridin-5(1 H )-one 71 in 60% yield ( Scheme 20 ) [ 51 ].…”

“… Synthesis of 3,7-dimethylchromeno[2,3- b ]pyrazolo[4,3- e ]pyridin-5(1 H )-one 71 [ 51 ]. Abbreviation: DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene.…”

Zn(OTf)2-Catalyzed Formal [3 + 3] Cascade Annulation of Propargylic Alcohols with 2-Aminochromones: Accessing the Chromeno[2,3-b]pyridines

“…Functionalized 4-oxo-4 H -chromones are of particular utility because they belong to privileged medicinal scaffolds and serve as key intermediates for the construction of a variety of novel heterocycles possessing diverse biological activities . Among the family of 4-oxo-4 H -chromones, the chromeno­[2,3- b ]­pyridine scaffold is a key skeleton that exists in many pharmacologically active molecules.…”