Regiospecific chlorination

Regiospecific chlorination of pyridine at the a-position occurs rapidly during irradiation in the presence of chlorine dissolved in carbon tetrachloride (67JHC375, 93AHC(58)274). Both ring and side-chain chlorination of 4-picoline occurs under 7-irradiation conditions (80JGU354). 

Lin S, Van Lanen SG, Shen B (2007) Regiospecific Chlorination of (S)-P-Tyrosyl-S-Carrier Protein Catalyzed by SgcC3 in the Biosynthesis of the Enediyne Antitumor Antibiotic C-1027. J Am Chem Soc 129 12432... 

The regioselective chloride loss from regiospecifically chlorine-37 enriched dichloro-, trichloro-, tetrachloro- and pentachlorodibenzofurans (149) was investigated under electron capture negative-ion chemical ionization conditions334. 

Regiospecific Chlorination and Oxygenation of Pentahydridodisilanyl Complexes of Iron and Ruthenium [1]... 

Keywords Metallo-Disilanes / Regiospecific Oxofiinctionalization / Regiospecific Chlorination... 

These products suggest a strong specific activation of the a-Si-H bond by the adjacent metal fragment. In addition, this effect determines the reaction of 4a-c with two moles of CCI4 leading to regiospecific chlorination of the a-silicon to give the ferrio- and ruthenio-dichlorodisilanes 6a-c (Scheme 3). 

Oxidations - 3,5-Dinitroperbenzoic acid is a stable storable peracid equivalent in activity to trlfluoroperacetic acid. A full paper has appeared which gives the experimental details for the a-hydroxylation of carbonyl compounds by treatment of the anions of enol silanes with Mo05 HMPA (MOOPH). Anions from carboxylic esters (LiN(iPr)2>LDA -78°C) can be efficiently, regiospecifically chlorinated or brominated by treatment with respectively CCl or CBr. Treatment of enol silanes from conjugated ketones with m-chloroperbenzolc acid (MCPBA) followed by removal of silicon affords the a-hydroxyketones. ... 

Regiospecific chlorination and bromination at the 5-position of 2-acetylthiophene has been achieved by converting it initially to the oximinoether and then halogenating it (molecular chlorine or bromine in the presence of Fe). Final hydrolysis of the oximinoether leads to the product <92S849>. 

The sulfur atom of thiophene can function as a template for radical-relay chlorinations. An excellent application of this concept is in the regiospecific chlorination of a steroid molecule <82JA2045>. Reaction of (2-thienyl)trichlorosilane with 3a-cholestanol gave the tris(cholestanyl)-silylether (623). When this was irradiated in CH2CI2 solution with 2 equiv. of sulfuryl chloride and a catalytic amount of AIBN, the 9(1 l)-olefin was produced in 45% yield after alkaline hydrolysis and elimination of HCl. Apparently, a chlorine atom becomes attached to the sulfur of the thiophene ... 

Aluminum chlorideioxygen nitrogen dioxide Regiospecific chlorination... 

Treatment of pyrrole, 1-methyl-, 1-benzyl- and 1-phenyl-pyrrole with one mole of A -bromosuccinimide in THF results in the regiospecific formation of 2-bromopyrroles. Chlorination with IV-chlorosuccinimide is less selective (8UOC2221). Bromination of pyrrole with bromine in acetic acid gives 2,3,4,5-tetrabromopyrrole and iodination with iodine in aqueous potassium iodide yields the corresponding tetraiodo compound. 

It has been shown that it is possible to compel regiospecific para substitution by enclosing the substrate molecules in a cavity from which only the para position projects. Anisole was chlorinated in solutions containing a cyclodextrin, a molecule in which the anisole is almost entirely enclosed (see Fig. 3.4). With a high enough concentration of cyclodextrin, it was possible to achieve a para/ortho ratio of 21.6 (in the absence of the cyclodextrin the ratio was only 1.48). This behavior is a model for the regioselectivity found in the action of enzymes. 

Ruppe S, A Neumann, W Vetter (2003) Anaerobic transformation of compounds of technical toxaphene. I. Regiospecific reaction of chlorobomanes with geminal chlorine aroms. Environ Toxicol Chem 22 2614-2621. 

Reduction of the heterocyclic ring and incorporation of a nitro function affords a compound with antischistosomal activity, oxamniquine (60). Its synthesis begins with chlorination of 2,6-dimethyl-quinoline, which proceeds regiospecifically on the methyl group adjacent to the ring nitrogen (56). 

Unsubstituted cycloamyloses have been used to catalyze a number of reactions in addition to acyl group transfer. Brass and Bender (8) showed that cycloamyloses promoted phenol release from diphenyl and bis(p-nitro-phenyl) carbonates and from diphenyl and bis(m-nitrophenyl)methyl phos-phonates. Breslow and Campbell (10,11) showed that the reaction of anisole with HOCL in aqueous solution is catalyzed by cyclohexaamylose and cycloheptaamylose. Anisole is bound by the cyclodextrins and is chlorinated exclusively in the para position while bound. Cycloheptaamylose has been used to promote regiospecific alkylation followed by the highly selective oxidation shown in reaction (3) (95). In addition cycloheptaamylose effec-... 

Scheme IV.71) shows the involvement of two chlorinating steps first, the chlorination of compound 179 at position 7 into 180, and second, the chlorination of 4-(2-amino-3-chlorophenyl)pyrrole (183) at position 3, forming 184. Two chlorinating enzymes responsible for these regiospecific chlorina-tions have been identified (85BBA181). 

Iron enneacarbonyl reacts smoothly with 1,1-dimethylsilacyclobutane to insert into the ring Si—C bond with complete regiospecificity (76JCS(D)910). The ferrosilacyclopentane (54) is thermally stable but reacts with HCl, and can also be prepared from 3-chIoropropyI-dimethylchlorosilane and Fe(CO)42. Carbonyl anions will substitute at silicon if this atom bears chlorine, and platinum will insert into the Si—H bond (Scheme 79) (72CC445, 78JOM( 144)317). 

Electrophilic addition of Cl., and In tn nlkenes is similar in mechanism to the electrophilic addition of Br0.46 The rate of chlorination in acetic acid is second-order, first-order each in olefin and in chlorine.47 Predominantly anti addition to alkyl-substituted double bonds occurs, indicating that a chloronium ion is formed.48 Further evidence for the chloronium ion is that addition of hypo-chlorous acid to double bonds is not entirely regiospecific. For example, addition to propene gives 91 percent of the Markownikoff product 29, and 9 percent of the anti-Markownikoff product, 30. Phenyl-substituted alkenes give a mixture of syn and anti adducts with Cl2 as they do with Br2.49... 

Dichloro-l,2-dithiole-3-thione (1) undergoes 1,3-cycloaddition with DMAD to give the adduct (2).1 On further heating with alkynes, regiospecific cycloaddition and molecular rearrangement occur with loss of chlorine to give 7//-thieno[2,3-c]thiopyran-7-thiones (3) and 4//-thieno[3,2-c]thiopyran-4-thiones (4). 

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