Abstract
The reaction of α-CF3-β-(2-nitroaryl) enamines with benzaldehydes afforded effectively α,β-diaryl-CF3-enones having nitro group. Subsequent reduction of nitro group by NH4HCO2-Pd/C system initiated intramolecular cyclization to give 2-CF3-3-benzylindoles. Target products can be prepared in up to quantitative yields. Broad synthetic scope of the reaction was shown. Probable mechanism of indole formation is proposed.
Highlights
In continuation of the investigation of α,β-diaryl-CF3-enones chemistry, in this article, we report synthesis of 2-CF3-3-benzylindoles by reduction of nitro group in α-(2nitroaryl)-β-aryl-CF3-enones followed by intramolecular cyclization (Figure 2)
We prepared a set of α-(2-nitroaryl)-β-aryl-CF3 -enones using recently elaborated by us synthetic protocol [64]
Condensation of α-CF3 -β-(2nitroaryl)enamines 1 with arylaldehydes 2 in acetic acid at 80–90 ◦ C led to the corresponding α-(2-nitroaryl)-β-aryl-CF3 -enones 3 in good to high yields
Summary
About 59% of small-molecule drugs are the derivatives of nitrogen heterocyclic compounds [24]. -3-benzylindoles by reduction of nitro group in α-(2-nitroaryl)ing of fluorinated building blocks, highly reactive small-molecules. In continuation of the investigation of α,β-diaryl-CF3-enones chemistry, in this article, we report synthesis of 2-CF3-3-benzylindoles by reduction of nitro group in α-(2nitroaryl)-β-aryl-CF3-enones followed by intramolecular cyclization (Figure 2). It should be noted, that 2-CF3-3-benzylindoles are quite a rare type of indoles. The copper-catalyzed C(sp2)-H trifluoromethylation of N,N-disubstituted hydrazones using the Togni’s reagent followed by Fischer indole benzylindoles were reported. In spite of the mentioned methods allowed to prepare 2-CF3 indoles in good yields (59–64%), low atom efficiency and high price of some used reagent should be taken into account (Figure 2)
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