5837-71-8Relevant articles and documents
Reversible Formation of Bromonium Ions. Preferential Reaction of Br(1-) on the Br(1+) of the Bromonium Ion Produced from the Solvolysis of the trans-2-Bromotriflate of Cyclohexane in MeOH or HOAc Containing Added Bromide
Zheng, C. Y.,Slebocka-Tilk, H.,Nagorski, R. W.,Alvarado, L.,Brown, R. S.
, p. 2122 - 2127 (1993)
The trans-2-bromotriflate of cyclohexane (4) has been solvolyzed at ambient temperatures in HOAc and MeOH containing varying and in the presence of 0.5M of a scavenger olefin, cyclopentene.The kinetics of solvolysis of 4 have been determined by observing the rate of change in color of an acid/base indicator that instantly responds to the production of HOTf or HBr.The kinetics show that the rate of solvolysis of 4 at constant ionic strength is independent of Br(1-).The products of solvolysis of 4 under the various conditions have been determined by quantitative GLPC analysis.In the presence of Br(1-), the products consisted of the trans 1,2-dibromides and bromosolvates of cyclohexane and cyclopentane.The cyclopentyl products are shown to be formed from the electrophilic addition of Br2/Br3(1-) to cyclopentene while trans-1,2-dibromocyclohexane (2) was obtained from Br(1-) capture of the bromonium ion of cyclohexene on carbon.The Br2 arises from capture by Br(1-) of the bromonium ion on Br(1+).On the basis of the ratio of the cyclopentyl products/2, Br(1-) capture of the solvolytically produced bromonium ion by attack on Br(1+) is 4-5 times more prevalent than attack on carbon in HOAc and ca. 25 times more prevalent than attack on carbon in MeOH.The results have strong implications on the reversal of bromonium ions formed during the electrophilic bromination of olefins in hydroxylic solvents.
Intermolecular Halogenation/Esterification of Alkenes with N-Halosuccinimide and Acetic Acid Catalyzed by 1,4-Diazabicyclo[2.2.2]octane
Pimenta, Laura S.,Gusevskaya, Elena V.,Alberto, Eduardo E.
supporting information, p. 2297 - 2303 (2017/07/07)
1,4-Diazabicyclo[2.2.2]octane (DABCO) is a suitable Lewis base that acts as an organocatalyst in the activation of N-chlorosuccinimide (NCS) towards the chlorination of alkenes. The chloriranium ion formed from NCS and the alkene, can be intermolecularly opened by a nucleophile, such as acetic acid, to produce highly functionalized trans-chloro esters in high yields. The protocol is also applied to the synthesis of chlorohydrins and chloro ethers using water or methanol as nucleophiles instead of acetic acid. Brominated analogs can also be synthesized from alkenes and N-bromosuccinimide (NBS) in the presence of various basic catalysts. However, the reaction patterns seem to be remarkably different. The catalytic performance of bases in the bromoesterification of alkenes was found to be strongly affected by their Br?nsted basicity, suggesting that acetyl hypobromite, formed in situ from NBS and acetic acid, acts as a real brominating agent in these systems. (Figure presented.).
Catalyst-free, direct, high regio- and chemoselective conversion of epoxides to vicinal haloesters under mild, neutral, and solvent-free conditions
Aghapour, Ghasem,Hatefipour, Razieh
, p. 1030 - 1040 (2013/03/14)
A catalyst-free, high regio- and chemoselective method is described for the mild conversion of wide varieties of epoxides directly to their corresponding vicinal haloesters using quaternary ammonium halides R4N +X- (X equa
Lipase-catalyzed kinetic resolution of 2-methylene-substituted cycloalkanols in batch and continuous-flow modes
Tomin, Anna,Hornyánszky, Gábor,Kupai, Katalin,Dorkó, Zsanett,ürge, László,Darvas, Ferenc,Poppe, László
experimental part, p. 859 - 865 (2011/12/15)
Kinetic resolutions of cyclic racemic secondary alcohols (2-methylenecyclopentan-1-ol rac-1a, 2-methylenecyclohexan-1-ol rac-1b, 2-methylenecycloheptan-1-ol rac-1c, 6-methylene-[1,3]dioxepan-5-ol rac-1d, 2,2-dimethyl-6-methylene-[1,3]dioxepan-5-ol rac-1e and trans-2-bromocyclohexan-1-ol rac-3) catalyzed by different (commercial and in-house-made) lipases were performed using vinyl acetate in THF-hexane. In the most typical cases (rac-1b, rac-1d and rac-3), the immobilized Candida antarctica lipase B (CaLB, for rac-1b and rac-3)- or sol-gel immobilized Pseudomonas fluorescens lipase (sol-gel LAK, for rac-1d)-catalyzed batch mode reactions were compared to the continuous mode reactions carried out in an enzyme-filled stainless steel bioreactor. The effect of temperature (20-60 °C) and flow rate (0.1-0.3 ml min-1) on the continuous-flow acetylation of rac-1b, rac-1d and rac-3 were investigated. In the kinetic resolutions of rac-1b, rac-1d and rac-3, the enantiomeric selectivities (E) were similar in the continuous-flow and batch (shake flask) modes. However, the productivities (specific reaction rate: r), were significantly higher in the continuous-flow mode biotransformations of rac-1b, rac-1d and rac-3.
