Microwave promoted palladium-catalyzed Suzuki–Miyaura cross-coupling reactions of 6-chloropurines with sodium tetraarylborate in water

Eco-Friendly Physical Activation Methods for Suzuki–Miyaura Reactions

“…The formation of a C-C bond at the 6-position of the electron-rich 1-,4-,6-trisubstituted benzimidazole nucleus is challenging and was not obtainable via Kumada, Negishi, Stille or Heck coupling strategies. As a result, Jain et al [48] have also focused their attention on the advantages of organotrifluoroborate salts as coupling partners for SMC with 4-nitro-6-triflyl benzimidazoles under MW activation in aqueous tetrahydrofuran (THF) [56]. Novel functionalization of 1-,4-,6-trisubstituted benzimidazoles at the 6-position was presented and 37%-70% yields were reported under 1-2 h of MW irradiation at 100 • C in the presence of PdCl 2 (dppf)·CH 2 Cl 2 (1 equiv.)…”

“…This SMC protocol was focused on the functionalization of the phenyl part of the oxindole core or the pyridine nucleus of the starting regioselective brominated or chlorinated spirooxindole moieties to give mono-or disubstituted-derivatives in good to excellent yields (70%-98%). Qu et al [48] have described a fast and sustainable process for the synthesis of 6-arylpurines from 6-chloropurines and sodium tetraarylborates via a MW assisted SMC reaction in water at 100 °C (Scheme 18). Furthermore, most of the reactions involved are efficient when using Pd(PPh3)2Cl2, 5 mol % catalyst in the presence of Na2CO3 (2 equiv.)…”

“…This eco-friendly MW-assisted method is a promising, green strategy for the preparation of these main nucleoside compounds. Qu et al [48] have described a fast and sustainable process for the synthesis of 6-arylpurines from 6-chloropurines and sodium tetraarylborates via a MW assisted SMC reaction in water at 100 °C (Scheme 18). Furthermore, most of the reactions involved are efficient when using Pd(PPh3)2Cl2, 5 mol % catalyst in the presence of Na2CO3 (2 equiv.)…”

Purine and Guanine Thioglycoside Analogs: Novel Synthesis of a New Class of Pyrazolo[1,5-a][1,3,5]Triazine-4-Thioglycoside Derivatives under Microwave Activation

“…Thioguanine inhibits purine biosynthesis as does 6-MP, albeit at different steps. [3] 6-MP and 6-TG are the only two purine anti-metabolites that are currently used in chemotherapy. [4] 6-MP and 6-TG have certain therapeutic disadvantages, which have continued to stimulate the search for purine analogs enhancing therapeutic efficacy.…”

“…The key step of this protocol is the formation of sodium pyrazolo [1,5-a] [1,3,5]triazine-4-thiolates via condensation of 5-amino-1H-pyrazoles with sodium cyanocarbonimidodithioate salt under microwave irradiation, followed by coupling with halo sugars to give the corresponding purine thioglycoside analogues. Further studies on the application of this method for the synthesis of other highly functionalized biologically active glycosides are underway.…”