A green approach for efficient α-halogenation of β-dicarbonyl compounds and cyclic ketones using N-halosuccinimides in ionic liquids

Understanding Organic Processes in Ionic Liquids: Achievements So Far and Challenges Remaining

“…This indicates an increase in the polarity of the nitrogen-bromine bond, indicating an electrophilic mechanism and explaining the observed order of reactivity. A similar argument has been used to account for the increased rate of halogenation of β -dicarbonyl compounds and cyclic ketones by N-halosuccinimides (Scheme 7) [79]. mi crowave (16) Scheme 9.…”

Halogenation of organic compounds in ionic liquids

“…This method also proved to be efficient for bromination of the nucleoside bases, uracil and cytosine, while the purine bases, adenine and guanine, were reported to be resistant to this protocol. 82 63 Reactions performed for 10-60 min at room temperature and without any catalyst afforded the corresponding a-brominated products in high yields (88-95%). a-Bromination of aryl ketones and 1,3-dicarbonyl compounds was also reported in [bmim] [BF 4 ] with NBS in the presence of UHP, which was used to activate the brominating reagent.…”

“…Yadav et al reported its efficient utilization for aromatic ring iodination of various arenes activated towards electrophilic functionalization 64 and for a-iodination of cyclic ketones and b-dicarbonyl compounds (Table 19). 63 81 The iodination step with NIS was performed at room temperature for electron-rich substrates, namely anisole, dimethylaniline, thiophene and mesitylene. Less reactive substrates such as m-xylene required either heating at 80 C for 6-12 h or an acid catalyst in conjunction with NIS in the IL to afford the corresponding Heck-coupling product.…”

“…Comparison of various reagent systems in selected examples of chlorination of carbonyl compounds in ILs ambient temperature, without any other activator or catalyst, togive high yields of the corresponding a-halo-substituted carbonyl products 63. They attributed the enhanced reactivity of NXS reagents in IL to increased polarization of the N-X bond in the polar ionic medium and to stabilization of the charged ionic intermediates.It was mentioned that similar results could be obtained in a hydrophilic IL [bmim][BF 4 ] (Table 10, entries 3, 4, 6 and 7), but the authors preferred the hydrophobic medium [bmim][PF 6 ], from which the succinimide byproduct could be removed easily, thus enabling IL recycling and reuse.…”

Efficient one-pot synthesis of ethyl 2-substitued-4-methylthiazole-5-carboxylates

“…The conventional synthesis of 4a usually starts from ethyl acetoacetate (1) and N-bromosuccinimide (NBS) (20)(21)(22) in dichloromethane to give the intermediate ethyl 2-bromo-3-oxobutanoate (2), which was then reacted with thiourea (3a) to give the target molecule (4a) (Scheme 1; 23). This two-step synthesis of 4a was limited by the tedious work-ups and low overall yield (11%; 24).…”