Antarafacial-Antarafacial Cope Rearrangement
نویسندگان
چکیده
Thermal rearrangement of 2-thiabicyclo[ 3.2.0]hepta-3,6-diene-6,7-dicarbonitriles 1-3 to their 4,5-dicarbonitrile isomers 4-6 takes place at 110-140 "C in yields of 82-84%. The reactions are first order with rates almost independent of the polarity of the solvent. Activation parameters (m = 120-140 kJ mol-' and AS* = 0 J K-l mol-') are in agreement with a concerted symmetry-allowed antarafacial-antarafacial Cope rearrangement. Compounds 1-3 rearrange photochemically via cleavage of the C-1-S bond to the 1,7-dicarbonitrile isomers 7-9. Isomer 9 rearranges further on prolonged irradiation to give 10. A tentative mechanism for this rearrangement is given.
منابع مشابه
Helicoid shiftamers.
We report calculations on the activation barriers for antarafacial [1,7]-hydrogen shifts in various helical polyenes containing saturated substructures. Based on these calculations, we predict that the barrier for analogous hydrogen shifts in the infinite system-a [1,7]-shiftamer-is only approximately 14 kcal/mol if the reactant is preorganized in an appropriate helical conformation.
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