3- Bromo-l-hexene

Describe simple chemical tests that would distinguish between (a) benzene and toluene (b) bromobenzene and bromocyclohexane (c) bromobenzene and 3-bromo-l-hexene ... 

The aryl halide may be distinguished from the alkene by the failure of the former to decolorize bromine in carbon tetrachloride and by the failure to decolorize cold, dilute, neutral permanganate solutions. 3-bromo-l-hexene undergoes a reaction with these reagents as shown below ... 

As with any intermediate, a transient radical can be implicated from products formed in a reaction specific to the radical of interest. Experimentally, this is the basis of so-called mechanistic probe studies. An application of this method might employ, for example, 6-bromo-l-hexene as a probe for a radical intermediate as shown in Figure 4.3. If the 5-hexenyl radical is formed as a transient with an adequate lifetime, then cyclization of this radical to the cyclopentyhnethyl radical could eventually give the cyclic product, and detection of the cyclic product provides evidence that a radical was formed. The mechanistic probe approach is deceptively simple, however. To be useful, one must exclude other possibilities for formation of the rearranged product and demonstrate that the transient was formed in the reaction of interest and not in a side reaction. The latter is especially difficult to demonstrate, and, unfortunately, some mechanistic probe studies that seemingly provided proof of radical intermediates were later found to be complicated by radical-forming side reactions. 

There is also the possibility that one combination of reactants will give more isomeric products than the other. For example, this may occur when electron-donating substituents are present in the olefinic reactant. This effect is seen in the reciprocal reactions of methyl /3-bromomethacrylate with 1-hexene and of Z-l-bromo-l-hexene with... 

For example, addition of 1,3-dibromopropane to the THF solution of 8 at — 78"C formed the intermediate 9a, which cyclized, when warmed to room temperature, to yield 1-methyl-l-(l-methylethenyl)cyclopentane 13 [11]. On the other hand, an acidic workup of 9a at — 35 C gave a single monoalkylated product, 6-bromo-2,3,3-trimethyl-l-hexene 12, in 72% isolated yield. Similar chemistry was observed with 1,4-dibromobutane, except that no cyclization would occur without refluxing conditions. Interestingly, the cyclization of 9a to 13 represents a cross-coupling of an organomagnesium reagent with an alkyl bromide, which is normally observed only in the presence of certain transition metal salts or complexes [12]. 

A mechanistic study concerning the variation of the product ratio in reactions of different o-(3-butenyl)halobenzenes (Hal = F, Cl, Br and I), and of 6-bromo-l-hexene with different alkali metals (Li, Na, K) in ammonia/tert-butyl alcohol solution 110) is related to the problem of anion versus radical cyclization as outlined in this chapter. 

Bromo-3-propyl-l-hexene (longest chain that contains double bond is six carbons)... 

Vinyl bromide 22 (n = 0) gave 61% of acetylene 23 (n = 0), for example, but 1-bromo-l-hexene (22, n = 4) gave only 18% of the corresponding alkyne (23, n = 4).29 Alkynes can also be formed from nonterminal (internal) vinyl halides (such as 3-bromo-3-heptene), but when alkoxide bases are used, the vigorous conditions usually required for elimination of the halogen can cause the triple bond of the product to migrate to the terminal position.30... 

It must be emphasized that isomerization of a probe can be taken as positive evidence for a radical intermediate in a substitution reaction, but failure to observe cyclization with such a probe does not rule out a radical intermediate. For example, reaction of 6-bromo-l-hexene with NaSN(CH3)3 in THF was found not to produce cyclized product. CycHzed product was observed when the same reaction was carried out in 1 1 THF-pentane, however. ° These results suggested that cyclization of the radical probe occurs outside the solvent cage in which it is formed and that a lower viscosity solvent allows more radicals to diffuse from the radical cage so that cyclization can occur. 

Bromo-l-hexene, B-60264 (Bromomethyl)cyclopentane, B-70241 5-Bromo-3-methyl-1 -pentene, B-60299... 

Ca. 50% excess 6-bromo-l-hexene heated 3 hrs. at 130° in benzene with tributyltin hydride and di-tert-butyl peroxide as initiator in a sealed degassed tube methylcyclopentane. Y ca. 80-90%. F. e. C. Walling and A. Cioffari, Am. Soc. 94, 6059 (1972). 

This procedure illustrates a general method for the stereoselective synthesis of ( P)-disubstitnted alkenyl alcohols. The reductive elimination of cyclic /3-halo-ethers with metals was first introduced by Paul3 and one example, the conversion of tetrahydrofurfuryl chloride [2-(chloromethyl)tetrahydrofuran] to 4-penten-l-ol, is described in an earlier volume of this series.4 In 1947 Paul and Riobe5 prepared 4-nonen-l-ol by this method, and the general method has subsequently been applied to obtain alkenyl alcohols with other substitution patterns.2,6-8 (I )-4-Hexen-l-ol has been prepared by this method9 and in lower yield by an analogous reaction with 3-bromo-2-methyltetra-hydropyran.10... 

As in the Negishi reaction, various alkylboron reagents have also been successfully coupled with electrophile partners. Suzuki et al. coupled 1-bromo-l-phenylthioethene with 9-[2-(3-cyclohexenyl)ethyl]-9-BBN (27), prepared by a simple addition of 9-borabicyclo[3.3.1]nonane (9-BBN) to 4-vinyl-1-hexene (26), to furnish 4-(3-cyclohexenyl)-2-phenylthio-1-butene (28) in good yield [36],... 

Chloro-3-hexei -l-yne and 5-Bromo-3-hexen-l -yne from 3-Hydroxy-4-hexen-I-vne and Concentrated Aqueous HQ or HBr... 

One of the classical solutions to overcome the low reactivity is to render the carbomagnesiation intramolecular. For example, Utimoto and coworkers reported that the reaction of ( )-6-bromo-3-methyl-l-trimethylsilyl-l-hexene (85) with magnesium produces the corresponding Grignard reagent 86, which intramolecularly adds to the vinylsilane moiety from the less hindered side affording a single stereoisomer of cycUzed product 87 (Scheme 60) °°. 

Butene 1-Bromo-3,3-dimethyl-l-fluoro- E10b2. 101 (Educt) 1-Hexene 1-Bromo-2-fluoro- ElOa, 239 (In + EBr) ElOb,. 375 (In I HE/N-Br — amine)... 

Bromochlorination of olefins such as 1-hexene, ethylene, 3,4-dichloro-l-butene, trans-l,4-dichloro-2-butene and 3-chloro- and 3-bromo-propene has been accomplished using... 

The effect of chain length on the catalytic performance was investigated using a series of co-bromo-2-methylalkenes. In all cases the predominant enantiomer produced had the -configuration except for 3-bromo-2-methylpropene oxide, which was predominantly in the S-form due to the priority switch [274], The short propene and butene derivatives were converted quantitatively whereas the longer pentene, hexene and heptene substrates failed to convert completely. Many other functional groups such as carboxylic ester, methoxy, acetoxy and carbonic ester are accepted by the system. The epoxidation fails, however, for 4-hydroxy-2-methyl-l-butene as substrate [270]. 

The second synthesis of lasubine II (6) by Narasaka et al. utilizes stereoselective reduction of a /3-hydroxy ketone O-benzyl oxime with lithium aluminum hydride, yielding the corresponding syn-/3-amino alcohol (Scheme 5) 17, 18). The 1,3-dithiane derivative 45 of 3,4-dimethoxybenzaldehyde was converted to 46 in 64% yield via alkylation with 2-bromo-l,l-dimethoxyethane followed by acid hydrolysis. Treatment of the aldol, obtained from condensation of 46 with the kinetic lithium enolate of 5-hexen-2-one, with O-benzylhydroxylamine hy-... 

As a result of an extensive study, it has been found that methylene groups are attacked much more readily than a methyl group. For example, 2-methyl-2-butene requires 16 hours for completion of the reaction, whereas, 2-methyl-2-hexene requites 10 minutes. The conversion of cyclohexene to 3-broraocyclohexene is accomplished in 20 minutes in 87% yield. It is noteworthy that the bromination of 1-octene with N-btomo-succinimide yields a mixture of l-bromo-2-octene and 3-bromo-1-octene and that the proportion of these isomers is in close agreement with the equilibrium mixture formed at 100° by analogous bromides. ... 

Bromo-3- 4-trifluoromethylphenyl)-3i/-diazirine (0.30 g, 1.1 mmol) was mixed with hex-l-ene (0.72 g, 8.6 mmol) and photolyzed for 5 h in a Pyrex tube with the light from a 200-W, focussed Osram XE Hg lamp. The reaction mixture was stirred magnetically, and the reaction temperature maintained at 25 °C by a water bath. Excess hexene was removed by simple distillation, and the residual oil was purified by chromatography (silica gel, pentane) yield 23.6 mg (7%). 

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