Dichloro dimer

DPXC ndDPXD. The economic pressure to control dimer costs has had an important effect on what is in use today (ca 1997). Attaching substituents to the ring positions of a [2.2]paracyclophane does not proceed with isomeric exclusivity. Indeed, isomeric purity in the dimer is not an essential requirement for the obtaining of isomeric purity, eg, monosubstituted monomer, in the pyrolysis. Any mixture of the four possible heteronucleady disubstituted dichloro[2.2]paracyclophanes, will, after all, if pyrolyzed produce the same monomer molecule, chloro- -xyljIene [10366-09-3] (16) (Fig. 4). 

Pasinszki and Westwood investigated the dimerization of chloronitrile oxide CICNO to 3,4-dichloro-l,2,5-oxadiazole-2-oxide 78 (Scheme 48) [98JPC(A) 4939]. From B3-LYP/6-31G calculations, they conclude that the reaction path can be characterized as a typical Firestone-type cycloaddition, a two-step mechanism with a C—C bond forming characterizing the first reaction step. The activation... 

Intramolecular acylnitrene-induced ring expansions of arenes are of great interest for the synthesis of novel 1//-azepines. Benzyl azidoformates, when subjected to spray-vacuum pyrolysis (SVP),152 yield l//,3//-oxazolo[3,4-a]azepin-3-ones which dimerize spontaneously 153,154 however, 2,6-dichlorobenzyl azidoformate yields the thermally stable (< 100 C) 5,9-dichloro-1 //,3//-oxazolo[3,4-a]azepin-3-one (8).154... 

On heating, the dichlorooxazolo[3,4- ]azepine 26, for which dimerization is prevented by the chloro groups, undergoes ring contraction and aromatization, involving a [l,2]-chlorine shift, to 5,8-dichloro-l,4-dihydro-2//-3,l-benzoxazin-2-one (27).11,153... 

The oxazolo[3,4-a]azepinones 4, in which 5 7 ring fusion imparts considerable planarity and hence antiaromatic character on the ring system, undergo spontaneous dimerization.153 The mode of dimerization appears to depend on the nature and position of substituents. The unsubstituted system and the 9-chloro derivative 4 (R1 = Cl R2 = H) produce the exo.anti-dimers, e.g. 5, upon spray-vacuum pyrolysis at 300 C, whereas the 7-/ert-butyl, 7-bromo, 7-methyl, and 7,9-dichloro (4, R1 = R2 = Cl) compounds yield the exo,syn-dimcrs, e.g. 6. 

In contrast, the 6,8-dichloro 7 and 6,8-dimethyl derivatives, in which [6 + 4] dimerization would locate a substituent at the bridgehead position, form the symmetrical [6+6] adducts, e.g. 8.154... 

The cyclic dimeric borazine derivatives 2 and 3 can be prepared by reaction of 2,4-dichloro-l,3,5,6-tetramethylborazine with aromatic 1,3-dihydroxy and l-amino-3-hydroxy compounds (Fig. 2). The products are obtained in yields... 

The incubation of 3,5-dichloro-4-methoxybenzyl alcohol with methanogenic sludge produced the de-O-methylated compound that was transformed to 2,6-dichlorophenol, and abiotically dimerized to fciX3,5-dichloro-4-hydroxyphenyl)methane (Verhagen et al. 1998) (Figure 2.2e). 

Sulphines may react as dienophiles with 1,3-dienes with the formation of cyclic sulphoxides. Unstable 2,2-dichloro-5,6-dihydro-2ff-thiin-l-oxide 191 was formed in an exothermic reaction between 173aandcyclopentadieneat — 40 (equation 101). The simplest, parent sulphine, CH2 = S = O, prepared in situ by treatment of a-trimethylsilylmethanesulphinyl chloride with cesium fluoride, reacts with cyclopentadiene to give bicyclic, unsaturated sulphoxide 192 as a mixture of two diastereoisomers in a 9 1 ratio (equation 102). On the other hand, a,j8-unsaturated sulphine 193 (generated by thermolysis of 2-benzylidene-l-thiotetralone dimer S-oxide) in boiling toluene behaves as a 1,3-diene and was trapped by norborene forming sulphoxide 194 in 78% yield ° (equation 103). 

An extremely pure product results, when difluorochloro methane or difluoro-dichloro methane are used as solvents (79). Dichlorophosphoric acid is a fluid, colourless, very hygroscopic liquid, which is easily soluble in CHCI3, CCI4, Ethanol and Ether (6). In the liquid phase it is stable for some time at room temperature, whereas at 12 Torr there is no sign of decomposition up to 250 °C (6). According to the Raman spectra in the liquid it is dimeric in analogy to the carboxylic acids (20) ... 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

Scheme 3 shows the details of the synthetic strategy adopted for the preparation of heteroleptic cis- and trans-complexes. Reaction of dichloro(p-cymene)ruthenium(II) dimer in ethanol solution at reflux temperature with 4,4,-dicarboxy-2.2 -bipyridine (L) resulted the pure mononuclear complex [Ru(cymene)ClL]Cl. In this step, the coordination of substituted bipyridine ligand to the ruthenium center takes place with cleavage of the doubly chloride-bridged structure of the dimeric starting material. The presence of three pyridine proton environments in the NMR spectrum is consistent with the symmetry seen in the solid-state crystal structure (Figure 24). 

The dichlororuthenium arene dimers are conveniently prepared by refluxing ethanolic ruthenium trichloride in the appropriate cyclohexadiene [19]. The di-chloro(pentamethylcyclopentadienyl) rhodium dimer is prepared by refluxing Dewar benzene and rhodium trichloride, whilst the dichloro(pentamethylcyclo-pentadienyl)iridium dimer is prepared by reaction of the cyclopentadiene with iridium trichloride [20]. Alternatively, the complexes can be purchased from most precious-metal suppliers. It should be noted that these ruthenium, rhodium and iridium arenes are all fine, dusty, solids and are potential respiratory sensitizers. Hence, the materials should be handled with great care, especially when weighing or charging operations are being carried out. Appropriate protective clothing and air extraction facilities should be used at all times. 

Almost 10 years later, Giidel et al. proposed a general synthetic method for facial tris cyclometalated Ir3+ and Rh3+ complexes by reaction of dichloro-bridged dimers of Ir(ppy)2 with excess ppy ligand using AgCF3S03 as a halide scavenger and promoter (Scheme 3.76) [289]. 

SCHEME 3.76 Schematic reaction to synthesis /ac-Ir(ppy)3 via dichloro-bridged dimers of Ir(ppy)2. 

Dichlorothiophenol is treated with chloroacetic acid to form 2,5-dichloro-phenylmercaptoacetic acid. Cyclization followed by oxidation with chlorosulfonic acid at 35°C affords 4,7-dichlorothionaphthenone-3. Direct addition of bromine in chlorosulfonic acid without separating the intermediate yields the 4,4, 1,1 -tetrachlorothioindigo derivative through oxidative dimerization. It is also possible to separate the monoheterocycle and to oxidize it with oxygen in an alkaline medium. 

Dichloro-2,2 -dimethyl-1,1 -dianthraquinonyl can be synthesized by Friedel-Crafts reaction from phthalic anhydride and 2,6-dichlorotoluene. Subsequent cyclization of the resulting substituted benzoylbenzoic acid 102 in sulfuric acid affords the corresponding anthraquinone derivative 103, which is dimerized by Ullmann reaction ... 

Dimers with a 1,2-bismethylenecyclobutane structure were obtained from 585 [240], 590 [238], 591 [241], 592 [242], 593 [243] and from the pinene derivative 597 [244]. The interception of 592 by 1,3-diphenylisobenzofuran (DPIBF) afforded two diastereomeric [4+ 2]-cycloadducts [245], Bicyclo[5.1.0]octa-3,4-diene (594) was generated by /3-elimination and trapped by sodium pyrrolidide because of the question of the extent to which the corresponding bicyclooctyne is formed in addition to 594 [184], Liberated by /3-elimination from ll,ll-dichloro-l,6-methano[10]annulene in... 

Chloro(phenylthio)carbene [32] has been produced by the standard phase-transfer catalytic procedure from PhSCHCK and trapped by alkenes (see Section 7.3), although the carbene is also prone to dimerization to give [PhS(Cl)C=C(Cl)SPhj. In a similar manner, phenylthiocarbene has been obtained from PhSCH2Cl [33] and chloro(phenoxy)carbene from dichloro(phenoxy)methane [34]. Reaction of the analogous seleno derivatives produce the conesponding phenylselenocarbenes... 

Figure 4. Cyclic voltairanograms for the oxidation of 2,6-dime thy1phenol, its dimer and tri-i-butylphenol at a platinum electrode, (a)-(c) in alkaline methanol, (d) in dichloro-methane.

Catalytic asymmetric methylation of 6,7-dichloro-5-methoxy-2-phenyl-l-indanone with methyl chloride in 50% sodium hydroxide/toluene using M-(p-trifluoro-methylbenzyDcinchoninium bromide as chiral phase transfer catalyst produces (S)-(+)-6,7-dichloro-5-methoxy-2-methyl-2--phenyl-l-indanone in 94% ee and 95% yield. Under similar conditions, via an asymmetric modification of the Robinson annulation enqploying 1,3-dichloro-2-butene (Wichterle reagent) as a methyl vinyl ketone surrogate, 6,7 dichloro-5-methoxy 2-propyl-l-indanone is alkylated to (S)-(+)-6,7-dichloro-2-(3-chloro-2-butenyl)-2,3 dihydroxy-5-methoxy-2-propyl-l-inden-l-one in 92% ee and 99% yield. Kinetic and mechanistic studies provide evidence for an intermediate dimeric catalyst species and subsequent formation of a tight ion pair between catalyst and substrate. 

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