Synthesis of 3(2)-phosphonylated thiazolo[3,2-a]oxopyrimidines

• Ksenia I. Kaskevich,
• Anastasia A. Babushkina,
• Vladislav V. Gurzhiy,
• Dmitrij M. Egorov,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2020, 16, 1947–1954, doi:10.3762/bjoc.16.161

• observed in the case of 6-trifluoromethyl-2-thiouracil that afforded 2- and 3-phosphonylated 5-oxothiazolopyrimidines in a 1:1 ratio. Keywords: chloroethynylphosphonate; heterocyclization; phosphonylated thiazolopyrimidines; phosphonylation; thiazolopyrimidine; 2-thiouracil; Introduction

• the latter [22][23][24][25][26][27][28]. Herein, we report the synthesis of a new series of phosphonylated thiazolopyrimidines. In our studies, chloroethynylphosphonate was used as the phosphonylating agent, which allowed the formation of a thiazole ring with simultaneous phosphonylation of the latter

• analysis. It is important to note, that the reaction of dimethyl 2-chloroethynylphosphonate (2a) with 2-thiouracil had some features. The reaction proceeded with the formation of a mixture of 7-oxo and 5-oxo isomers in a ≈1: 0.1–0.3 ratio. However, a decrease in the signal of the 7-oxo isomer was observed

Synthesis of ([1,2,4]triazolo[4,3-a]pyridin-3-ylmethyl)phosphonates and their benzo derivatives via 5-exo-dig cyclization

• Aleksandr S. Krylov,
• Artem A. Petrosian,
• Julia L. Piterskaya,
• Nataly I. Svintsitskaya and
• Albina V. Dogadina

Beilstein J. Org. Chem. 2019, 15, 1563–1568, doi:10.3762/bjoc.15.159

• equimolar ratio of the starting reagents and anhydrous K2CO3 at room temperature. The reaction progress was monitored by 31P NMR spectroscopy. A complete conversion of chloroethynylphosphonate was achieved after 4 hours of reaction (Scheme 2). Note the reactions of 2-hydrazinylpyridines 1a–f with

• reaction mixture after the complete conversion of chloroethynylphosphonate promotes a Dimroth-like rearrangement of [1,2,4]triazolo[4,3-a]pyridine 10 into [1,2,4]triazolo[1,5-a]pyridine 12 completely (Scheme 4). Similar transformations have been observed in the reactions of 2-hydrazinylpyridines with ethyl

• nucleophilic substitution of chlorine in the chloroethynylphosphonate to form ynamine intermediate A, isomerization of which provides ketenimine B. Further formation of the imine tautomer C enables an intramolecular 5-exo-dig cyclization to furnish the title [1,2,4]triazolo[4,3-a]pyridines (Scheme 6