2- Methyl-2,4-dibromopentane

The reaction was carried out in a 1 L, three-necked flask fitted with a reflux condenser, thermometer, dropping funnel and mercury sealed stirrer. To the flask was added 100 mL water, 300 mL n-propyl alcohol and 196 g oxygen-free zinc dust prepared from commercial-grade zinc dust. The flask was placed in an ice-bath and 244 g (1 mol) of freshly distilled 2-methyl-2,4-dibromopentane was added dropwise with efficient stirring over a period of about 90 min. The icebath was then removed and the mixture was stirred at room temperature for about 32 h. After about 10 h an immiscible layer of hydrocarbon had formed. At the end of the reaction the hydrocarbon product was separated by distillation. The crude product 9 was collected over a temperature range of 49-51 °C and weighed 78.1 g, a yield of 86%. The refractive index of the crude product was 1.3847. The crude product was... 

This synthesis came shortly after one by Prelog, Kohlberg, Cerkovnikov, Rezek and Piantanida (1937) based on a series of reactions which, with modifications and extensions. Prelog and his colleagues have applied to the syntheses of bridged heterocyclic nuclei, of which this is an example. 4-Hydroxymethyltetrahydropyran (VI R =. OH) is converted via the bromo-compound (VI R = Br) and the nitrile (VI R = CN) into tetrahydropyran-4-acetic acid of which the ethyl ester (VII) is reduced to 4-()3-hydroxyethyl)-tetrahydropyTan (VIII). This is converted by fuming hydrobromic acid into 3-(2-bromoethyl)-l 5-dibromopentane (IX) which with ammonia in methyl alcohol yields quinuclidine (V). 

Alkylation of trifluoro- and trichloroacetamides with a-bromoacetic esters has been utilized for the synthesis of a wide range of a-aminoacetic acids [11-13] (Table 5.13). Hydrolysis of the intermediate a-trihaloacetamidoacetic esters with methanolic potassium hydroxide converts the methyl and ethyl esters directly into the amino carboxylic acids. /-Butyl a-aminoacetates are more stable, but they are hydrolysed under phase-transfer catalytic conditions (see Chapter 9.2). Reaction of the trihaloacetamides with 1,4-dibromobutane and 1,5-dibromopentane and subsequent hydrolysis provides a simple route to pyrrolidine-2-carboxylic acid (75%) and piperidine-2-carboxylic acid (58%) [11, 12],... 

The stereospecific C-alkylation of a range of benzylic ketones, such as tetralones, 2-phenylcyclohexanones and cycloheptanones, and 2-phenyl-y-lactones, has also been described [8]. For example, Af-(4-trifiuoromethylbenzyl)cinchonidinium bromide catalyses the reaction of 1,5-dibromopentane with 7-methoxy-l-methyl-2-tetralone to yield the (R)-l-(5-bromopentyl) derivative (75% yield with 60% ee). 

Alternatively, six-membered-ring halonium ions were also formed when equimolar amount of 1,5-dihalopentane was added to dihalonium ions [Eq. (4.122)]. The dihalonium ions were prepared from 1,5-dihalopentane and 2 mol of methyl fluor-oantimonate. Furthermore, the dimethylbromonium ion 129-Br is also a sufficiently active methylating agent to form cyclic pentamethylenebromonium ion 180-Br from 1,5-dibromopentane [Eq. (4.123)]. 

If another shorter alkane is attached to one of the nonterminal carbons, forming a branched alkane, the longest carbon chain forms the basis of the name, and the attached alkane is the prefix as shown in Figure 1.6. Figure 1.7 shows the structural formula of 2-methyl-2,3-dibromopentane in four steps. 

Figure 1.7. Structural formula of 2-methyl-2,3-dibromopentane (a) pentane is the major chain therefore, there is a straight saturated five-carbon chain as the major backbone (b) 2-methyl- there is a methyl group on the number two carbon (c) -2,3-dibromo dibiomo means two bromine atoms, and they are on the number 2 and 3 carbons (d) the rest of the bonds are not specified therefore, they are all bonded to hydrogen thus we have 2-methyl-2,3-dibromopentane.

Hardacre and Doherty described the synthesis and use of OSs supported bis(oxazolines) in various copper catalyzed reactions such as Diels-Alder reaction [97] and Mukaiyama-Aldol reactions [98], Starting from mono methyl substituted box ligand, deprotonation followed by alkylation using an excess of dibromopentane provided the required alkyl halide for quatemarisation. After ion metathesis the imidazolium supported box ligand (L12) is isolated in a good 62% overall yield (Fig. 30). 

In both methods 1 and 2, the hydrochloride salts are converted to the zwltterlon with anion exchange resin (0H form). The tetrahydrothlophene substitution goes essentially all para to the phenolic hydroxy. If the para position is blocked, the tetrahydrothlophene substitutes In the ortho position no meta substitution has been observed. Phenolic compounds that have electron-withdrawing groups (such as Cl) will not react under conditions of either method 1 or 2. Chlorine-containing derivatives may be prepared by chlorination of the appropriate zwitterion hydrochloride (9 ). Six mend>ered cyclic sulfonium zwitterions can be prepared in only very low yields by methods 1 and 2. These compounds may be obtained by the reaction of 1,5-dibromopentanes with 4-(methylthio)phenol in refluxing chlorobenzene to yield the sulfonium salt and methyl bromide (method 3) 9). Ifethod 3 is also applicable to the preparation of meta substituted derivatives (13). 

Preparation by reaction of 1,5-dibromopentane with 2-hydroxy-4-mercapto-3-propylacetophe-none in the presence of potassium carbonate and potassium iodide in refluxing methyl ethyl ketone [2271]. 

The two stereoisomers of 3-methyl-2,4-dibromopentane shown below were cyclized by treatment with zinc in 1-propanol-water. The products were analyzed for the ratio of cis- to trans- nvae hy -cyclopropanes the results are as follows ... 

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