Directed regioselectivity of bromination of ketones with NBS: solvent-free conditions versus water

The reaction conditions employed directed the site of functionalisation of ketones with NBS: under solvent-free conditions α-bromination was the exclusive process, while in water, ring functionalisation occurred in the case of methoxy substituted aromatic ketones.     

流动注射化学发光测定硫酸小诺霉素及其机理探讨

在碱性介质中,硫酸小诺霉素能被N 溴代琥珀酰亚胺(NBS)氧化,在荧光素的增敏作用下,产生化学发光。基于此,建立了测定痕量硫酸小诺霉素的流动注射化学发光分析法。硫酸小诺霉素在0.5～100μg·mL-1的浓度范围内与化学发光强度呈良好的线性关系,检出限(3σ)为0.08μg·mL-1,对5μg·mL-1的硫酸小诺霉素连续测定11次,相对标准偏差为1.8%。将本方法用于制剂中硫酸小诺霉素的分析,结果满意。     

NBS-assisted an efficient conversion of styrenes to α-hydroxy ketones in water

An expedient, mild and environmentally benign method for the oxidation of styrenes to α-hydroxy ketones has been developed. This conversion has been achieved by employing water as a solvent as well as an oxygen source. This facile and efficient tandem process provides α-hydroxy ketones in moderate to good yields from easily accessible styrenes.     

NBS-mediated synthesis of β-keto sulfones from benzyl alcohols and sodium arenesulfinates

An efficient synthetic route towards the synthesis of β-keto sulfones has been developed from secondary benzyl alcohols using N-bromosuccinimide (NBS). The present protocol utilizes NBS as oxidant as well as brominating agent, readily accessible benzyl alcohols and sodium arenesulfinates as the sulfonylating reagent under mild conditions. The control experiments revealed that the reaction proceeds via oxidation of alcohol to ketone, α-bromination of ketone and nucleophilic substitution by sodium arenesulfinate. Furthermore, the efficiency of the methodology was tested with a gram scale reaction and also shown the synthetic utility.     

N-Bromosuccinimide assisted oxidation of 5-aminopyrazoles: formation of bis diazenylderivatives

Treatment of 5-amino-4-cyanopyrazoles with N-bromosuccinimide, in DMF at rt gave azo dyes resulting from dimerization through the amino groups and further oxidation.With bromine water the dimer was also formed but, bromination occurred on the aryl ring, either at reflux or rt. Reduction of the azo group with zinc in acetic acid originated the corresponding pyrazoles.     

Syntheses and structures of missing links among polybromocyclopentadienyl rhenium and manganese tricarbonyl complexes

Reactions of diazocyclopentadiene and NBS at appropriate stoichiometries give 2,5-dibromodiazocyclopentadiene and 2,3,5-tribromodiazocyclopentadiene in 40% and 30% yields, respectively, after chromatography. These react with BrRe(CO)₅ or BrMn(CO)₅ (80 °C, CF₃C₆H₅) to give (η⁵-1,2,3-C₅H₂Br₃)M(CO)₃ (3; M = a, Re; b, Mn) and (η⁵-C₅HBr₄)M(CO)₃ (4a,b) in 75-85% yields. In the case of 4a, the intermediate η¹-cyclopentadienyl complex (η¹-C₅HBr₄)Re(CO)₅ (4′a) can be isolated (44%). An isomer of 3b, (η⁵-1,2,4-C₅H₂Br₃)Mn(CO)₃, is accessed by desilylating previously reported (η⁵-1,2,4-C₅(SiMe₃)₂Br₃)Mn(CO)₃ with CsF/MeOH (85%). The reaction of tetrabromodiazocyclopentadiene and BrRe(CO)₅ at 80 °C in CF₃C₆H₅ gives the η¹-cyclopentadienyl complex (η¹-C₅Br₅)Re(CO)₅ (5′a, 74%) which cannot be induced to decarbonylate to (η⁵-C₅Br₅)Re(CO)₃ (5a) under a variety of conditions. However, 5a can be isolated (45%) when a similar reaction is conducted at 120 °C. The IR properties of the preceding complexes are compared, and the crystal structures of 3a, 3b, 5a, and 5′a are determined and analyzed.     

Flow injection determination of cationic surfactants by using N-bromosuccinimide and N-chlorosuccinimide as new oxidizing agents for luminol chemiluminescence

Two highly sensitive chemiluminescence (CL) systems are described. The method is based on the CL generated during the oxidation of luminol by N-bromosuccinimide (NBS) and N-chlorosuccinimide (NCS) in alkaline medium. The emission intensity is reduced by the presence of some surfactants at concentrations lower than critical micelle concentration (cmc).A new, simple, rapid and selective flow injection CL method for the determination of cationic surfactants such as dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) is proposed. Their determinations are based on the reducing effect on the emission intensity of NBS-luminol and NCS-luminol chemiluminescent reactions. The effect of analytical and flow injection analysis (FIA) variables on these CL systems and on the determination of the cationic surfactants are discussed. The optimum parameters for the determination of cationic surfactants were studied and were found to be the following: luminol, 1×10⁻⁶ M; NBS and NCS both, 5×10⁻² M; NaOH, 5×10⁻² M and flow rate, 3.5 ml min⁻¹.     

Metal triflate catalyzed highly regio- and stereoselective 1,2-bromoazidation of alkenes using NBS and TMSN3 as the bromine and azide sources

Metal triflate catalyzed 1,2-bromoazidation of alkenes was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN₃) as the bromine and azide sources, respectively. Among the metal triflates, Zn(OTf)₂ was found to be the best catalyst. This catalytic process represents a highly regioselective, stereoselective and high yielding method for the synthesis of anti-1,2-bromoazides from a variety of alkenes including α,β-unsaturated carbonyl compounds.     

Ultrasound-assisted synthesis of 2-amino-1,3,4-oxadiazoles through NBS-mediated oxidative cyclization of semicarbazones

A ultrasound-assisted oxidative cyclization of semicarbazones using N-bromosuccinimide in the presence of sodium acetate was established providing efficient and rapid access to a variety of 2-amino-1,3,4-oxadiazoles. Moreover, the new synthetic protocol provides a simple procedure utilizing a safer oxidizing system that affords the target products in high regioselectivity, satisfactory yields, and elevated purities.