Bromination of cyclopropanes using potassium bromide and cerium(IV) ammonium nitrate (CAN): synthesis of 1,3-dibromides

Ring-Opening Functionalization of Simplegem-Difluorocyclopropanes by Single-Electron Oxidants

“…When KI was employed instead of KBr, the formation of the corresponding iodopropanol 4l′ was realized in a high yield. Dibromopropane and other unidentified byproducts were also observed by 19 F NMR measurement. In case of bromoamidation, it was interesting to note that the corresponding Scheme 3.…”

“…Bromohydroxylation and Bromoamidation Table 2. Reactivity Difference between 1d and 1h a a The numbers in brackets were determined by 19 F NMR analyses. For obtaining further information on the reaction mechanism, the present dibromination was performed in the dark (Scheme 4a), which allowed to decrease the yield of the dibrominated butane 2a from 86% under the standard conditions to 45% with a larger amount of the side product, tribrominated 3a in 26% yields.…”

“…Unless otherwise mentioned, the NMR spectra for 1 H, 13 C, and 19 F were recorded at 300, 75.5, and 282 MHz, respectively, in CDCl 3 unless otherwise noted on a JEOL JMN AL-300, with chemical shifts being reported in parts per million downfield from internal TMS (δ: 0.00) for 1 H, CDCl 3 (δ: 77.0) for 13 C{ 1 H} NMR, and BTF (δ: −64.00) or C 6 F 6 (δ: −163.00) for 19 F NMR spectra. Data were tabulated in the following order: a number of protons or fluorines, multiplicity (s, singlet; d, doublet; t, triplet; q, quartet; quint, quintet; m, multiplet; br, broad peak), and coupling constants in Hertz.…”

“…Because we have recently found out a more convenient preparation method of F 2 CPs starting from methyl 2,2-difluoro-2-(fluorosulfonyl)­acetate and styrene derivatives by a slight modification of the Dolbier’s procedure, utilization of these products was explored at the next step for the demonstration of their synthetic importance as potent building blocks. With reference to the reported method on the Br radical-promoted (di)­bromination of alkenes as well as nonfluorinated cyclopropanes, our own modification led to a facile and mild protocol, which was affected by a mixture of KBr and CAN. This transformation realized not only 1,3-dibromination but also 1,3-bromohydroxylation as well as 1,3-bromoamidation just from simple F 2 CPs without any special structural devices (Scheme ).…”

Boron tribromide as a reagent for anti-Markovnikov addition of HBr to cyclopropanes

“…11 Compared to activated cyclopropanes, 12 oxidative functionalization of unactivated cyclopropanes gives a wide range of useful molecules that are otherwise not readily accessible, and protocols for the Markovnikov-selective functionalization of unactivated cyclopropanes have been reported. [13][14][15][16][17][18][19][20] Halolyses of cyclopropanes to give 1,3-dihaloalkanes by molecular halogens are also documented although the reactions commonly suffer from the formation of side products via electrophilic aromatic halogenation. 21 In contrast, obtaining products with anti-Markovnikov regioselectivity has been considered as one of the top challenges in industry.…”