Chlorination regioselectivity

Dong, C., Flecks, S., Unversucht, S. et al. (2005) Tryptophan 7-halogenase (PrnA) structure suggests a mechanism for regioselective chlorination. Science, 309, 2216-2219. 

Boyes and Wild reported the manganese-mediated regioselective chlorination of allenes [14]. For the dichlorination of cyclo-l,2-nonadiene, the dichloride was obtained as the major product whereas the reaction of monosubstituted allene afforded a mixture of regiosomers of the dichlorination products with 2,3-dichloro-1-alkene 12 being the major one. The yield with oxalyl chloride is better than that with TMSC1. 

Hough, and Richardson s regioselective chlorination of the 3 -OH of methyl p-lactoside following regioselective... 

The first efforts toward the regioselective chlorination of sucrose came with John... 

Richardson and Hough s efforts on the chlorination of sucrose ran in parallel with their studies on the selective chlorination of other readily available disaccharides. One notable piece of work done with Philippe L. Durette involved a study of the regioselective chlorination of methyl (S-maltoside (Scheme 31), which was undertaken with the long-term objective of possibly developing a future synthesis of the natural antitumor agent, amicetin. 

Regioselective chlorination at C-5 of 3-pivaloyloxymethylpyrido[4,3- pyrimidine A -oxide 198 with POCI3 (100°C/2h) gave 199 via a Meisenheimer A -oxide rearrangement (Equation 15)<2004TL3737>. 

Furthermore, di- and polychlorination are much less prevalent. Dicarboxylic acids are predominantly chlorinated in the middle of the chain,99 and adamantane and bicy-clo[2.2.2]octane at the bridgeheads100 by this procedure. The reasons for the high to - 1 specificity are not clearly understood.101 Alkyl bromides can be regioselectively chlorinated... 

Regioselective chlorination of aromatics. Phenol undergoes regioselective chlorination at the orf/io-position with 1, but selectivepara-chlorinationwith2. Chlorination of anisole by either reagent results exclusively in para-chlorination, because of steric effects.2 Chlorination of naphthol with 1 and 2 is more regioselective than that of phenol.1... 

Dong C, Flecks S, Unversucht S, Haupt C, van Pee K-H, Naismith JH (2005) Tryptophan 7-Halogenase (PmA) Structure Suggests a Mechanism for Regioselective Chlorination. Science 309 2216... 

A. K. Norton and M. von Itzstein, The synthesis of 6-substituted methyl l-O-acetyl-3,4-anhydro-jS-D-tagatofuranosides. Regioselective chlorination and thioacetylation in the presence of an oxiran, Aust. J. Chem., 49 (1996) 281-283. 

PhICl2 is the chlorinating agent in the novel template directed radical relay process of remote regioselective chlorination of steroids introduced by Breslow. In this method a... 

Regioselective chlorination of toluene is not observed under the above conditions but the ortholpara ratio can be controlled over a reasonable range (0.52-2.85) by altering the acidity of the solvent766 and the nature of the parent amine767. 

Regioselective chlorination. This N-chloroammonium salt (1) as well as N-chlo-ropiperidine, chlorinates aromatic compounds substituted with an electron-donating group with high para-selectivity. Benzene and toluene are attacked only slowly. 

RCH2-CH2CH2SO2NHR are converted primarily to RCHCICH2CH2SO2NHR by sodium peroxydisulfate Na2S20g and For regioselective chlorination at... 

An alternative synthesis of the tungsten bis-silanol A starts with the regioselective chlorination of the metal-bound Si-H function of 6 with PdCli. The corresponding tungsten chlorosilane 9 is isolated in 85% yield as a yellow solid (Scheme 2). 

Monodechloroaminopyrrolnitrin 3-halogenase catalyzes the regioselective chlorination of the aminophenylpyrrole derivative monodechloroaminopyrrolnitrin to aminopyrrolnitrin116, however, nothing is known about the substrate specificity of this enzyme. 

Regioselective chlorination, bromination, nitration by hexachloro-cyclohexadienone reagents or 4-nitro-cyclohexadienone 5 (see 1 st edition). 

The regioselective chlorination of unsymmetrical ketones at the more substituted -position has also been carried out using aqueous... 

Hydroxylation of the a-silicon in ferriodisilanes has been tried in the case of the dichloro(ferrio)disilanes 9a,b, obtained from the ferriodisilanes 3a,b via regioselective chlorination with CCI4 [6]. However, only in the case of 9a treatment with water in the presence of EtsN succeeded in the generation of the ferriodihydroxydisilane 10 after 14 h in 81 % yield (Eq. 4). 

Chloro-2(lH)-quinoxalinone 6 the precursor of 2,6-dichloroquinoxaline was our first target. Several methods have been carefully evaluated to prepare this key intermediate which represents the most expensive part of our molecule. The simplest method would certainly be the regioselective chlorination of 2(lH)-quinoxalinone (5). However, the halogenation in acetic acid is known to occur mainly at position 7, (2). Only recently, a direct chlorination of 6 in concentrated sulphuric acid in the presence of silver sulphate has been reported to afford exclusively 6-chloro-2(lH)-quinoxalinone in 51% (3). 

The direct regioselective chlorination of unprotected hexitols and pentitols by Vilsmeier-Haack reagent (Me2N =CHCl Cl ) has been described For example, D-glucitol was converted, (following acetylation) into 5. Some 2,3,5-tri-6>-acetyl-l,4-anhydro-6-chloro-6-deoxy-D-glucitol was also formed. 

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