Bromo-2-heptene

Submitted by F. L. Greenwood, M. D. Kellert, and J. Sedlak.1 Checked by John D. Roberts and A. T. Bottom. 

Tn a50()-ml. round-bottomed flask lilted with a stirrer, nitrogen inlet tube, and reflux condenser are placed -10 g. (0.103 mole) of 

2-heptene, 48.1 g. (0.272 mole) of N-bromosuccinimide, 0.2 g. of benzoyl peroxide, and 250 ml. of carbon tetrachloride (Note 1). The reaction mixture is stirred and heated under reflux in a nitrogen atmosphere for 2 hours (Note 2). The succinimide is removed by suction filtration, washed twice with 15-ml. portions of carbon tetrachloride and the carbon tetrachloride washings are combined with the filtrate (Note 3). The carbon tetrachloride solution is transferred to a 500-ml. Claisen flask modified so that the distilling arm carries a 25 x 300 mm. section packed with glass helices. The capillary is attached to a source of nitrogen and the carbon tetrachloride removed at 36-38°/190 mm. (Note 4). 

The residue is transferred to a 125-ml. Claisen flask modified so that the distilling arm carries an 18 x 180 mm. section packed with glass helices. Nitrogen is led into the capillary, and, after a forerun of 1-3 g., there is collected 28-31 g. (58-64%) of 4-bromo-2-heptene, b.p. 70-71°/32 mm., 1.4710-1.4715 (Note 5). A residue of 7-10 g. remains in the distilling flask (Note 6). 

The 2-heptene was the pure grade material purchased from Phillips Petroleum Company, Bartlesville, Oklahoma. This olefin is comparable to material prepared by a Boord synthesis. The N-bromosuccinimide was obtained from Arapahoe Chemicals, Inc., Boulder, Colorado. The benzoyl peroxide was used as received from Distillation Products, Rochester, New York. The carbon tetrachloride was reagent grade, from J. T. Baker Chemical Company, Phillipsburg, New Jersey. 

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The above procedure is applied to 2-heptene (9.8 g, 0.1 mole), 11.5 g (0.066 mole) of NBS, and 0.1 g of benzoyl peroxide in 50 ml of carbon tetrachloride. The mixture is refluxed with stirring for 2 hours. Final fractionation yields 50-65% of 4-bromo-2-heptene, bp 70-71732 mm. 

Bromo-2-heptene, 38, 8 a-Bromoisobutyryl bromide, 33, 29 -Bromomandelic acid, 36,11 2-Bromo-3-methylbenzoic acid, 38,... 

When first distilled, the product is nearly colorless. On standing under nitrogen in the refrigerator for several days, the material acquires a pale yellow color. Evidence for the identity of the product as 4-bromo-2-heptene is outlined in reference 3. 

Ziegler and coworkers 2 indicated that allylic methylene groups undergo bromine substitution more readily than allylic methyl groups. This has been shown 3 to be true, and the treatment of 2-heptene with N-bromosuccinimide gives rise to 4-bromo-2-heptene. 

Heptenc reacts with NBS to give primarily a mixture of 4-bromo-2-heptene Md 2-bromo-3-heptene. Use SpartanView to examine the two radicals A and B. ... might form in the reaction, identify the radical that leads to the observed products, and explain why this radical forms preferentially. 

The reaction of 3-bromo-5-(methylthio)-2-methylselenophene (61) with ethyllithium and ethyl bromide (Eq. 18) gives mixed thioselenoacetals of an acetylenic ketene (62) in high yield.80 Similarly, isomeric 3-bromo-5-methyl-2-(methylthio)selenophene (63) is also easily cleaved to give 2-ethylseleno-5-methylthio-2-hepten-4-yne (64) (Eq. 17). Such compounds are difficult to obtain by other methods. 

The presence of Me3Sn and Me3Ge radicals was ascertained by reactions of the lithio reagents with cyclopropylcarbinyl bromide and 6-bromo-l-heptene, whereupon products of free radical reactions were produced along with those from direct displacement. 

The reaction of bornyl and isobornyl bromides with the nucleophile (Scheme 18) is another case where the amount of inversion is small and the rate constant close to that observed with an aromatic anion radical of the same standard potential (Daasbjerg et al., 1989) it can therefore be rationalized along the same lines. Cyclizable radical-probe experiments carried out with the same nucleophile and 6-bromo-6-methyl-1-heptene, a radical clock presumably slower than the preceding one, showed no cyclized coupling product. It should be noted, on the other hand, that, unlike the case... 

TABLE 3. Cycloproparenes from l-bromo-6-chlorobicyclo[4.1.0]heptenes Compound Yield (%) Ref. Compound Yield (%) Ref. 

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 reaction of Ph3MLi (M = Ge, Sn) or Me3SnNa with 6-bromo-l-heptene gave the expected 6-Mi4-l-heptene as the major product, but also (2-methylcyclopentyl)methyl derived metal-14 compound (equation 92)137. An intermediate l-methyl-5-hexenyl radical was proposed, but its participation was not clearly established. Distannylation of haloalkylpropene was also described (equation 93)138. 

Alkaline and alkaline earth metal-14 compounds TABLE 9. Reaction profile of R3MLi with 6-bromo-l-heptene... 

Intramolecular 6-exo-radical cyclization of 7-bromo-3-methoxy-l-methylthio-1 -(p-tolylsulfonyl)-1 -heptene (66) exhibited a highly efficient 1,2-asymmetric induction to yield the trans ring-closure product 67 (Scheme 17).45 Also reported are radical cyclizations ofy-oxygenated-a,P-unsaturated sulfones, often with very high observed stereoselectivity.45,46... 

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