Reaction of α-Bromo Enones with 1,2-Diamines. Cascade Assembly of 3-(Trifluoromethyl)piperazin-2-ones via Rearrangement

Synthesis of 5-(trifluoroacetyl)imidazoles from Bromoenones and Benzimidamides via Aza-Michael Initiated Ring Closure Reaction

INTRODUCTION

A simple method for the preparation of 5-(trifluoroacetyl)imidazoles was elaborated.

METHODS

The reaction of trifluoromethyl(α-bromoalkenyl)ketones with benzimidamides was employed to afford the target heterocycles in good yields.

RESULTS

The assembly of imidazole core proceeds via aza-Michael adduct formation followed by intramolecular nucleophilic substitution and spontaneous aromatization as an oxidation sequence.

CONCLUSION

The yields of target imidazoles can be improved by the use of soft oxidizing agents.

Synthetic utility of biomimicking vanadium bromoperoxidase and n-tetrabutylammonium tribromide (TBATB) in organic synthesis

Nature has established a broad spectrum of methods to introduce halogen atoms in organic compounds. Recent developments have revealed that haloperoxidases are one of the major sources responsible for incorporating bromines to produce bromoorganics in nature. Pioneering studies of numerous researchers have unravelled the details of haloperoxidases, mainly vanadium dependent enzyme bromo- and iodo-peroxidases, including reaction mechanism, kinetics and especially biomimicking studies. In this review, we initially have described the scope of biomimicking vanadium bromoperoxidase in producing the bromonium ion and its further utilisation in conducting oxidative bromination or cleavage of various organic molecules. Moreover, by biomicmicking, the synthesis of OATB and the synthetic utility of various organic ammonium tribromides (OATBs) have been discussed. Among such OATBs, n-tetrabutylammonium tribromide (TBATB) has been explored for bromination of organic molecules as well as in the facile removal of several protecting groups and as a potential catalyst in various synthetic transformations. This review attempts to compile a myriad of reactions concerning the catalytic activity of vanadium bromoperoxidases and the usefulness of various OATBs, particularly with special emphasis on TBATB in various organic transformations.

An Efficient Synthesis of 2-CF3-3-Benzylindoles

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.

Modular Construction of Functionalized 2-CF3-Indoles

The reaction of α-CF3-β-(2-nitroaryl)enamines with benzaldehydes led to nitro-substituted α,β-diaryl-CF₃-enones in high yield. Subsequent reduction of the nitro-group to the amino moiety by the Pd/C-NH₄HCO₂ system resulted in intramolecular cyclization to form a 5-membered hemiaminal which is stabilized by the presence of a CF₃-group. The reaction of this hemiaminal with various nucleophiles afforded functionalized 2-CF₃-indoles isolated in up to quantitative yields. High efficiency and broad synthetic scope of all steps of the sequence were demonstrated. A possible mechanism of the reaction is discussed.

Synthesis of 4-arylamino-3-(trifluoromethyl)pyridazines and pyridazino[3,4-b]quinoxalines (as by-products) from 3-aroylmethyl-2-(trifluoromethyl)quinoxalines and hydrazine hydrate

A number of 4-arylamino-3-(trifluoromethyl)pyridazines were obtained in good yields via the novel reaction of 3-aroylmethyl-2-(trifluoromethyl)quinoxalines with an excess of hydrazine hydrate in refluxing n-butanol with or without acetic acid.

Unsaturated polyfluoroalkyl ketones in the synthesis of nitrogen-bearing heterocycles

This review focuses on the recent achievements and new developments in the synthesis of polyfluorinated aza-heterocycles based on fluorine-bearing enones and ynones published in the last decade.

Experimental and Theoretical Study of an Intramolecular CF3-Group Shift in the Reactions of α-Bromoenones with 1,2-Diamines

The reactions of trifluoromethylated 2-bromoenones and N,N'-dialkyl-1,2-diamines have been studied. Depending on the structures of the starting compounds, the formation of 2-trifluoroacetylpiperazine or 3-trifluoromethylpiperazine-2-ones was observed. The mechanism of the reaction is discussed in terms of multistep processes involving sequential substitution of bromine in the starting α-bromoenones and intramolecular cyclization of the captodative aminoenones as key intermediates to form the target heterocycles. The results of theoretical calculations are in perfect agreement with the experimental data. The unique role of the trifluoromethyl group in this reaction is demonstrated.

Reactions of CF3-enones with arenes under superelectrophilic activation: a pathway to trans-1,3-diaryl-1-CF3-indanes, new cannabinoid receptor ligands

CF₃-enones react with arenes in TfOH to givetrans-1,3-diaryl-1-CF₃indanes.

Access to novel imidazo[1,5-a]pyrazine scaffolds by the combined use of a three-component reaction and a base-assisted intramolecular cyclization

A novel and practical two-step approach to an intriguing class of imidazo[1,5-a]pyrazines with exocyclic C=X (X = CH2, O) bonds is described. The process utilizes a sequential three-component reaction of propargyl amine or aminoester, 1,2-diaza-1,3-dienes and isothiocyanates to furnish functionalized 2-thiohydantoins which are transformed into thiohydantoin-fused tetrahydropyrazines by subsequent regioselective base-promoted cyclization.