M Xylylene dibromide

Convenient routes to several new sterically crowded chelating diphosphines have been described.48-50 Thus, e.g., m-xylylene dibromide, on treatment with di-t-butylphosphine, affords a bisphosphonium salt, which on treatment with a weak base affords the diphosphine (58).48... 

Reactions of carbonyl compounds and imines. The salt 4 obtained from reaction of cinchonine with m-xylylene dibromide is shown to promote enantioselective transfer of the trifluoromethyl group from Me3SiCF3 to aryl ketones Also obtained from quinidine the salt containing a trifluorobenzyl group (5) promotes the condensation of chloromethyl phenyl sulfones with ArCFlO to give benzenesulfonyl epoxides ... 

Poly(xylylviologen) (PXV) was prepared from m-xylylene dibromide and 4,4 -bipyridine by the successive Menshutkin reaction in N,N-dimethylformamide (DMF) at 60 C for 72 h. PXV was obtained as precipitate in DMF solution after polymerization. The precipitate was filtered and washed with acetone to yield yellow powder after drying in vacuo. The intrinsic viscosity of PXV was 2.9 x 10" (dl/g) On 0.5 M KBr aqueous solution at 25 C) corresponding to the average molecular weight (j ) of about 8000 . 

Lithiated allyl sulfide 256-Li reacted with m-xylylene dibromide 257 to afford the bis-sulfide 258. A double Mislow-Evans rearrangement of 258 and subsequent reductive trapping of the sulfenate ester provided the symmetric trans-diol 255. Monoprotection, Sharpless asymmetric epoxidation, and reductive ring-opening of the epoxide gave 1,3-diol 259 in 97% ee. After several functionalizations, the arene was subjected to Birch reduction to provide 1,4-cyclohexadiene 254. Ozonolysis of the diene, followed by reductive workup and treatment of the resulting 1,3-diketone with acid furnished pyra-... 

Nucleophilic substitution of O-protected dibromide 13a with tosylamide and NaH base gave a 13 % yield of the homoazacalix[4]arene 75, next to 10 % yield of the [3,3]cyclophane 76 [48]. On the other hand, 2-fluoro-m-xylylene dibromide under similar circumstances gave 25 % [3,3]cyclophane 77 and only 3.7 % of the homoazacalix[3]arene 78 (Fig. 16.6) [53]. In the same way, starting from cyana-mide and 13a, mixtures of the corresponding [3,3]cyclophane 76 (R = CN) and homoazacalix[4]arene 75 (R = CN) were formed (Fig. 16.6) [54]. 

A solution of 52.8 g. (0.20 mole) of o-xylylene dibromide (Note 6) in 300 ml. of purified dimethylformamide is added dropwise with stirring at such a rate as to maintain a temperature of 60-70° (Note 7). Subsequently the reaction mixture is stirred at room temperature for 3 hours and then poured into 600 ml. of ice water in a 2-1. Erlenmeyer flask. After standing at room temperature overnight the product is collected by suction filtration, pressed on the funnel, and washed twice with 100-ml. portions of water. The crude product is air-dried on filter paper for 2-3 hours and is then dissolved in 1.21. of boiling 95% ethanol. The solution is filtered through a heated funnel, and the filtrate is refrigerated overnight. The crystals are collected on a Buchner funnel and washed on the funnel with 100 ml. of cold 95% ethanol. The product is dried over phosphorus pentoxide in a vacuum desiccator. The yield of white crystals of 2-(% tolylsulf onyl)-dihydroisoindole is 41-46 g. (75-84%), m.p. 174-175° (dec.). 

Precautions to be observed in handling o xylylene dibromide are described in Org. Syntheses, Coll. Vol. 4, 984 (1963). The dibromide was purchased from Eastman Organic Chemicals, recrystallized from 95% ethanol (3 ml./g.), and dried over potassium hydroxide in a vacuum desiccator, m.p. 89-91°. 

Ji-Toldaldehyde, 2-bromo-, 46,13 />-ToJuenesult onamide, alkylation with o-xylylene dibromide, 47, 111 -Toluenesulfonvlbromide, 45, 88 -Toluenesulfonyl chloride m prepara tion of methvl isocyanide, 46,... 

The conformational flip is in part influenced by the presence of bulky internal (C2-) substituents. A case in point is the exclusive formation of 215sf from a coupling between the diphenolic cuppedophane 186 and p-xylylene dibromide [Eq. (21)]. The presence of a bromine atom at the internal position is believed to be responsible for the flip of the phenolic rings, leading to the sole formation of 215sf. It has been previously observed in solid state structures of cuppedophanes [20] that a conformational flip of wall component rings occurs if the m-terphenyl unit bears internal bulky substituents (see Fig. 1). 

Bria et al. synthesized a tetracationic cyclophane-aromatic crown ether-type side-chain poly[2]catenane 59 by employing click chemistry, via route iii (Scheme 17.18) [111]. First, the template-directed coupling reaction between bis(bipyridinium) salt 28 and the alkyne-substituted p-xylylene dibromide 55, in the presence of dinaphtho crown ether 54, afforded an alkyne-functionalized [2]catenane 56 [112], Substitution of the chloro group on styrene-vinylbenzyl chloride copolymer 57 (M = 3.7 kDa, M , = 6.3 kDa) with sodium azide gave the azide-functionalized polymer 58 [83,113-115]. By employing CuS04/ascorbic acid as catalyst [116-120], click chemistry between azide-functionaUzed polymer 58 and alkyne-functionalized [2]catenane 56 afforded the side-chain poly[2]catenane 59, the successful formation of which was confirmed with Fourier transform infrared (FTIR) and NMR analyses. Unfortunately, both of these techniques revealed that the reaction of the azide groups was incomplete, and the observation was ascribed to a Coulombic repulsion of the cyclophane units and steric hindrance caused by the bulky catenane units[121]. 

Treatment of dibromide (102) with magnesium gave a moderate yield of the octa-fluoro[4,2]paracyclophane, but the cyclization was less successful for a tetrafluoro-analogue. " m-Dichlorobenzene and 2,6-dichloropyridine have been coupled in the presence of a nickel catalyst with the bis-Grignard reagents derived from a,a)-dibro-moalkenes to prepare [n]metacyclophanes and [n](2,6-pyridinophanes (n = 6—12) in fair yields. Muscopyridine (103) was thus obtained (20% yield). [2"]Paracyclo-phanes (n = 3—6,8) have been prepared by treatment of p-xylylene chloride with sodium in THF and their n.m.r. spectra used to study conformational changes. The... 

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