Bookser, Brett C. published the artcileSolvent-Controlled, Site-Selective N-Alkylation Reactions of Azolo-Fused Ring Heterocycles at N1-, N2-, and N3-Positions, Including Pyrazolo[3,4-d]pyrimidines, Purines, [1,2,3]Triazolo[4,5]pyridines, and Related Deaza-Compounds, Application In Synthesis of 1268520-92-8, the publication is Journal of Organic Chemistry (2018), 83(12), 6334-6353, database is CAplus and MEDLINE.
Alkylation of 4-methoxy-1H-pyrazolo[3,4-d]pyrimidine (1b) with iodomethane in THF using NaHMDS as base selectively provided N2-Me product 4-methoxy-2-methyl-2H-pyrazolo[3,4-d]pyrimidine (3b) in an 8/1 ratio over N1-Me product (2b). Interestingly, conducting the reaction in DMSO reversed selectivity to provide a 4/1 ratio of N1/N2 methylated products. Crystal structures of product 3b with N1 and N7 coordinated to sodium indicated a potential role for the latter reinforcing the N2-selectivity. Limits of selectivity were tested with 26 heterocycles which revealed that N7 was a controlling element directing alkylations to favor N2 for pyrazolo- and N3 for imidazo- and triazolo-fused ring heterocycles when conducted in THF. Use of 1H-detected pulsed field gradient-stimulated echo (PFG-STE) NMR defined the mol. weights of ionic reactive complexes. This data and DFT charge distribution calculations suggest close ion pairs (CIPs) or tight ion pairs (TIPs) control alkylation selectivity in THF and solvent-separated ion pairs (SIPs) are the reactive species in DMSO.
Journal of Organic Chemistry published new progress about 1268520-92-8. 1268520-92-8 belongs to pyrazoles-derivatives, auxiliary class Other Aromatic Heterocyclic,Chloride, name is 4-Chloro-1-methyl-1H-pyrazolo[3,4-b]pyridine, and the molecular formula is C7H6ClN3, Application In Synthesis of 1268520-92-8.
Referemce:
https://en.wikipedia.org/wiki/Pyrazole,
Pyrazoles – an overview | ScienceDirect Topics