New approach toward the synthesis of deuterated pyrazolo[1,5-a]pyridines and 1,2,4-triazolo[1,5-a]pyridines

A Simple and Easily Implemented Method for the Regioselective Introduction of Deuterium into Azolo[1,5-a]pyrimidines Molecules

A method for the technically easy-to-implement synthesis of deuterium-labeled pyrazolo[1,5-a]pyrimidines and 1,2,4-triazolo[1,5-a]pyrimidines have been developed. The regioselectivity of such transformations has been shown. ¹H NMR and mass spectrometric methods have proved the quantitative nature of such transformations and the kinetics of deuterium exchange has been studied. Spectrally, at different temperatures (+30 °C, -10 °C and -15 °C), the kinetics of the process was studied both in CD₃OD and in deuterated alkali.

Oxidative [3+2]Cycloaddition of Alkynylphosphonates with Heterocyclic N-Imines: Synthesis of Pyrazolo[1,5-a]Pyridine-3-phosphonates

A series of pyrazolo[1,5-a]pyridine-3-ylphosphonates were prepared with moderate to good yields by the oxidative [3+2]cycloaddition of 2-subtituted ethynylphosphonates with in situ generated pyridinium-N-imines and their annulated analogs. 2-Aliphatic and 2-Ph acetylenes demonstrate low activity, and the corresponding pyrazolopyridines were achieved with a moderate yield in the presence of 10 mol% Fe(NO₃)₃·9H₂O. At the same time, tetraethyl ethynylbisphosphonate, diethyl 2-TMS- and 2-OPh-ethynylphosphonates possess much greater reactivity and the corresponding pyrazolo[1,5-a]pyridines, and their annulated derivatives were obtained with good to excellent yields without any catalyst. 2-Halogenated ethynylphosphonates also readily reacted with pyridinium-N-imines, forming complex mixtures containing poor amounts of 2-halogenated pyrazolopyridines.

Potassium tert-Butoxide Promoted Regioselective Deuteration of Pyridines

A regioselective deuteration at β- and γ-position of pyridines is reported. Efficient deuteration occurred with a combination of KOtBu and DMSO-d6, replenishing the prevailing α-deuteration of pyridine systems. Preliminary mechanistic...