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The Preparation and Properties of Thermo-reversibly Cross-linked Rubber Via Diels-Alder Chemistry
Published on: August 25, 2016
Electrostatic interactions between substituents as regioselectivity control elements in Diels-Alder cycloadditions. A
Gregori Ujaque1, Joseph E Norton, K N Houk
1Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, California 90095-1569, USA.
Abstract:
The regioselectivities of Diels-Alder reactions of 1-methoxy-4-trimethylsiloxy-1,3-butadiene and the corresponding o-xylylene with acrylonitrile were explored with density functional theory. The transition state of the reaction of the diene with acrylonitrile was studied in both the gas phase and in a low dielectric (epsilon = 2.247) solvent. The regioselectivities of these reactions are predicted to be controlled by the direct electrostatic interactions between the diene and dienophile substituents. The electron-donating capacities of methoxy and trimethylsiloxy substituents are shown to be very similar and to not contribute to regioselectivity control. A prediction is made that the cycloadditions of the o-xylylene will be unselective, while 1-methoxy-4-trimethylsiloxy-1,3-butadiene will give a small preference ( approximately 5:1) in favor of the proximal methoxy and cyano groups. The thermochromic behavior of trans-disubstituted disiloxy benzocyclobutene was also explored.
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