C–H cycloamination of N-aryl-2-aminopyridines and N-arylamidines catalyzed by an in situ generated hypervalent iodine(iii) reagent

Abstract

A metal-free synthesis of diversified pyrido[1,2-a]benzimidazoles and 1H-benzo[d]imidazoles from N-aryl-2-aminopyridines and N-arylamidines has been developed. The C-H cycloamination reaction was catalyzed by hypervalent iodine(III) species generated in situ from iodobenzene (catalytic) and peracetic acid (stoichiometric). The reaction proceeded smoothly at ambient temperature to provide the corresponding N-heterocycles in good to excellent yields.

Hypervalent Iodine(III) Promoted Direct Synthesis of Imidazo[1,2‐a]pyrimidines

“…However, in contrast to PIDA, use of PIFA in a mixture of CH 3 CN and AcOH with or without copper triflate led to decreased yields (Table 1, Entries 8–9). In comparison, the hypervalent iodine(III) formed in situ from catalytic iodobenzene and stoichiometric m ‐chloroperbenzoic acid ( m ‐CPBA), a strategy applied by Antonchick for the efficient intramolecular C(sp 2 )–H bond amination reaction,14 afforded either no desired product in CH 3 CN (Table 1, Entry 10) or a very low yield with HFIP as solvent (Table 1, Entry 11) 11…”

“…Despite significant achievements in their synthesis, development of highly efficient approaches to diversified imidazo[1,2‐ a ]pyrimidine derivatives from readily available starting materials continues to be an active and rewarding research area. Recently, Zhu and co‐workers reported an elegant synthesis of imidazo[1,2‐ a ]pyridines from readily accessible N ‐aryl‐2‐aminopyridines by catalysis of an in situ generated hypervalent iodine reagent by using 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) as the indispensable solvent 11. As a part of our continuing interests in the chemistry and biologically activity of pyrimidine‐containing compounds,12 we herein describe an efficient hypervalent iodine promoted intramolecular C–H bond cycloamination reaction to give imidazo[1,2‐ a ]pyrimidine derivatives in good yields from readily available N ‐aryl‐2‐aminopyrimidines or pyrimidyl enamines.…”

Benzimidazopurine nucleosides from N6-aryl adenosine derivatives by PhI(OAc)2-mediated C–N bond formation, no metal needed

“…5–7 Of relevance to the present work are the approaches to synthesis of benzimidazoles and azabenzimidazoles using hypervalent iodine reagents. Examples include cyclizations of appropriate precursors with PhI/CH 3 CO 3 H, 8 PhI(OAc) 2 or PhI(OTFA) 2 , 9–11 PhI(OAc) 2 / m -CPBA/ p -TsOH or Koser’s reagent, 12 and rearrangements of N -benzyl-2-aminopyridines. 13 …”

Oxidative Heterocycle Formation Using Hypervalent Iodine(III) Reagents

“…Analogously, in 2014, Chiba and coworkers reported an efficient hypervalent iodine enabled diastereoselective anti-aminooxygenation and anti-diamination of N-allylamidines 20 for the synthesis of dihydroimidazoles 21 [22]. Zhu and coworkers [23] developed a metal-free intramolecular C-H amination reaction of N-aryl-2-aminopyridines 22 catalyzed by a hypervalent iodine(III) species generated in situ from iodobenzene and peracetic acid for the synthesis of pyrido[1,2-a]benzimidazoles 23 (Scheme 5). Interestingly, the authors published [24] another paper showing that pyridobenzimidazoles 23 can also be obtained from N-benzyl-2-aminopyridines 24 in the presence of PhI(OPiv) 2 as a stoichiometric oxidant in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) via an oxidative tandem demethylenation cycloamination reaction (Scheme 5).…”