title: Four-component bicyclization approaches to skeletally diverse pyrazolo[3,4-b]pyridine derivatives.
abstract: A novel four-component bicyclization strategy has been established, allowing a flexible and practical approach to 37 examples of multicyclic pyrazolo[3,4-b]pyridines from low-cost and readily accessible arylglyoxals, pyrazol-5-amines, aromatic amines, 4-hydroxy-6-methyl-2H-pyran-2-one, and cyclohexane-1,3-diones. The polysubstituted cyclopenta[d]pyrazolo[3,4-b]pyridines were stereoselectively synthesized through a microwave-assisted special [3+2+1]/[3+2] bicyclization with good control of the spatial configuration of exocyclic double bonds. The novel [3+2+1]/[2+2+1] bicyclization resulted in 17 examples of unreported pyrazolo[3,4-b]pyrrolo[4,3,2-de]quinolones. Reasonable mechanisms for forming two new types of multicyclic pyrazolo[3,4-b]pyridines are also proposed.
authors.affiliation: School of Chemistry and Chemical Engineering, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials, Jiangsu Normal University , Xuzhou 221116, P. R. China.
authors.forename: Xing-Jun
authors.initials: XJ
authors.lastname: Tu
authors.forename: Wen-Juan
authors.initials: WJ
authors.lastname: Hao
authors.forename: Qin
authors.initials: Q
authors.lastname: Ye
authors.forename: Shuang-Shuang
authors.initials: SS
authors.lastname: Wang
authors.forename: Bo
authors.initials: B
authors.lastname: Jiang
authors.forename: Guigen
authors.initials: G
authors.lastname: Li
authors.forename: Shu-Jiang
authors.initials: SJ
authors.lastname: Tu
mesh_terms: D000588:Amines / Q000737:chemistry; D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D003500:Cyclization; D015394:Molecular Structure; D011720:Pyrazoles / Q000138:chemical synthesis* / Q000737:chemistry; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000588:Amines; D001643:Bridged Bicyclo Compounds; D011720:Pyrazoles; D011725:Pyridines; C447480:pyrazolo(3,4-b)pyridine