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|Title:||Synthetic Equivalents to Acetylene and Allene in the Diels-Alder Reaction|
|Author(s):||Stack, Dennis Patrick|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The use of cis- and trans-(beta)-halo acryloyl chlorides as dienophiles in the Diels-Alder reaction has been studied. The following dienes were employed: 9,10-dimethylanthracene, 2,3-dimethylbutadiene, isoprene, 2-phenylbutadiene, 1,2-diphenylbutadiene, cyclopentadiene, and 1,3-cyclohexadiene. With low molecular weight, volatile dienes, excess diene was used as the solvent while hydrocarbon solvents, such as hexane or heptane, were used in the cycloaddition reactions with high molecular weight, non-volatile dienes. Owing to the powerful activating effect of the acyl chloride functionality, only relatively short reaction times and temperatures ranging from 25 to 100(DEGREES)C were required. Adducts derived from 9,10-dimethylanthracene, and 1,2-diphenylbutadiene were obtained as crystalline solids, easily purified by recrystallization from hexane or hexane-chloroform mixtures. On the other hand, adducts derived from 2-phenylbutadiene, cyclopentadiene, 2,3-dimethylbutadiene, isoprene, and 1,3-cyclohexadiene were, in most cases, oils that were efficiently purified by distillation under reduced pressure.
Reductive fragmentation of the (beta)-halo acyl chlorides, which were obtained from the Diels-Alder reactions, with bis(triphenylphosphine)-nickel dicarbonyl in aromatic hydrocarbn solvents removed the activating functional groups at the (alpha),(beta)-positions and generated the desired carbon-carbon double bonds. Reductions that afforded high molecular weight hydrocarbons were carried out in benzene at 80(DEGREES)C. The syntheses of volatile hydrocarbons, on the other hand, were conducted in 1-methylnaphthalene at 90(DEGREES)C and the products were swept from the reaction vessel with a nitrogen stream. From this reaction, nine hydrocarbon products were produced in yields ranging from 17 to 93%. The combination of the cycloaddition reactions of the (beta)-halo acryloyl chlorides with 1,3-dienes and the subsequent reductive elimination reaction constitutes a new synthetic equivalent to acetylene.
In a similar fashion, 2-(bromothyl)acryloyl bromide was used as a synthetic equivalent to allene. This acid bromide was employed as a dienophile in Diels-Alder reactions with 9,10-dimethylanthracene, trans, trans-1,4-diphenylbutadiene, and cyclopentadiene. These primary, (beta)-bromo acyl bromides were also reduced efficiently with the same nickel(O) reagent forming the desired exocyclic double bonds. Three hydrocarbon products were furnished from this aspect of this research in yields ranging from 52 to 88%.
The mechanism of the reductive fragmentations probably involves acylation of a coordinatively unsaturated nickel(O) species followed by subsequent rearrangement to an alkylnickel intermediate. The organonickel intermediate could then fragment to form the double bond by a variety of pathways. One possibility would be the heterolytic fragmentation of the (beta)-haloalkylnickel intermediate in an ElcB like mechanism. On the other hand, trans-(beta)-halo alkylnickel intermediates could undergo a cis-elimination of a nickel hydride complex which could then reduce the resulting vinyl halide in subsequent reactions. In the case of cis-(beta)-haloalkylnickel intermediates, cis-elimination of a nickel halide species would form the double bond directly.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-13|