1-Hexene, vinylic substitution productions

Table III. Vinylic Substitution Productions from 1-Hexene and Various Vinylic Bromides and Morpholine ...

Several approaches were taken. Capillary-column gas chromatography on a vinylation reaction product showed 24 separate peaks present in the hexenyl acetate fraction however, six of the peaks accounted for about 90% of the total sample. Hydrogenation of the reaction mixture (hydrogen over platinum on carbon) reduced the hexenyl acetates to a mixture of three hexyl acetates and thereby greatly simplified determining the position of oxygen substitution with, however, loss of information on olefin position. We tried to synthesize the specific hexenyl acetate isomers by the ester interchange reactions (Reactions 7a, 7b, and 7c). Mixtures of isomers were obtained, but they corresponded to the main components of the vinylation reaction mixture. For example, the main products isolated from the vinylation of hexene-1 corresponded to the products from Reactions 7a and 7b—i.c., vinyl rather than allyl esters. 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

In addition, the vinyl radical can rearrange, before accepting an electron and a proton, to afford either a cis or trcms alkene as a final product. Among compounds that have been investigated are aryl-substituted vinyl bromides [96], cis- and tra w-3-iodo-3-hexene [97], bromomaleate and bromofumarate [98], and aryl-substituted 3-chloroacrylonitriles [99]. Yoshida and coworkers [100] electrolyzed vinyl halides at platinum in DMF in the presence of trimethylchlorosilane to obtain silylation products. 

The reactions and product distributions thus far reported have been exclusively concerned with hexene. It was of interest to see whether the high specificity of positional substitution could be maintained with the other hexene isomers. By positional substitution specificity is meant ester attachment on ether of the carbons involved in the original carbon-carbon double bond. Table VII shows the results of these studies. The internal olefins reacted more slowly than the a-olefin, and with both palladium chloride-cupric chloride and 7r-hexenylpalladium chloride-cupric chloride systems high substitutional specificity (> 95% ) was also maintained with 2-hexene (Table VII). However, with 3-hexene the specificity is considerably lower (80%). Whether this is caused by 3-hexene isomerization prior to vinylation or by allylic ester isomerization is not known. A surprisingly high ratio of 2-substitution to 3-substitution is found ( 7 1) in the products from 2-hexene. An effect this large... 

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