TBAI-catalyzed oxidative coupling of aminopyridines with β-keto esters and 1,3-diones—synthesis of imidazo[1,2-a]pyridines

Abstract

TBAI could catalyze the direct oxidative C-N coupling of 2-aminopyridines with β-keto esters and 1,3-diones, which affords imidazo[1,2-a]pyridines as the products. The reaction was realized under metal-free conditions by using tert-butyl hydroperoxide (TBHP) as the oxidant.

Retraction: tert‐Butyl Hydroperoxide and Tetrabutylammonium Iodide‐ Promoted Free Radical Cyclization of α‐Azido‐N‐arylamides

“…[13] Following this work, we reported that a-substituted bacetyl amides could be converted to a-keto amides via oxidative C À C bond cleavage by treatment with CuCl 2 /BF 3 ·OEt 2 /TBHP under an oxygen atmosphere. [14] On the basis of these results, we hoped that the TBHP-based oxidizing systems might be used to turn a-azido-N-phenylacetamides into a-(aminocarbonyl)iminyl radicals under metal-free conditions.…”

Temperature-controlled NaI-mediated α-oxybenzoylation or oxyacylation–decarboxylation reactions of dimethyl malonate with carboxylic acids

“…On the basis of previous work in the literature [30][31][32] and our own results described above, we proposed a plausible mechanism for the present reactions, which is shown in Scheme 4. Iodide was initially oxidized by TBHP to Na[IO] − , which was further oxidized to a key intermediate hypoiodite Na[IO 2 ] − (A) with one more equivalent of TBHP [33,34].…”

Recent synthetic scenario on imidazo[1,2-a]pyridines chemical intermediate

“…Further, a similar reaction was reported using tert-butyl hydroperoxide (TBHP) as the terminal oxidant and tetrabutylammonium iodide (TBAI) as a catalyst (Scheme 5) [37,38]. Next, they reduced alkyl imidazo[1,2-a]pyridine-2-caboxylates 1.36 and 1.37 into the corresponding alcohols 1.38 and 1.39, which can be utilized to transform into the anxiolytic drugs saripidem 1.4 and necopidem 1.3, respectively (Scheme 6) [39].…”