Thermodynamic vs. kinetic control in the Diels-Alder cycloaddition of cyclopentadiene to 2,3-dicyano-p-benzoquinone: Kinetic control revisited

Study of all stages of the Diels–Alder reaction of cyclopentadiene with 2,3‐dicyano‐1,4‐benzoquinone and monoadducts: Kinetics, thermochemistry, and high pressure effect

“…The structures of monoadducts ( 3 ) and ( 4 ) were determined previously 7,8 . The structure of 3,10‐dioxopentacyclo[10.2.1.1 5,8 .0 2,11 .0 4,9 ]hexadeca‐6,13‐diene‐2,11‐dicarbonitrile ( 5 , Scheme 1) was confirmed by the single‐crystal X‐Ray experiments.…”

“…However, the difference in the enthalpy of reaction does not always determine the difference in the Diels–Alder reaction rate 34 . The change in the reaction rate constant with the active C 2 ═C 3 bond of dienophile 2 with cyclopentadiene (457, Table 1), 9,10‐dimethylanthracene (235) 8 and quadricyclane (36.9 L mol −1 s −1 ) 14 does not follow the change in enthalpy of these reactions: −79.4 (Table 2), −50, 13 and −182.2 kJ mol −1 , 14 respectively. The enthalpies of the reaction of tetracyanoethylene with these dienes vary in the following way: −113, −88, and −236 kJ mol −1 .…”

“…8 123–124°C). 1 H and 13 C NMR spectra of monoadducts ( 3 ) and ( 4 ) were the same as previously described 8 . White crystals of bisadduct ( 5 ), 3,10‐dioxopentacyclo[10.2.1 1,12 .1 5,8 .0 2,11 .0 4,9 ]hexadeca‐6,13‐diene‐2,11‐dicarbonitrile, were obtained from solution of 2 with the large excess of diene ( 1 ), m.p.…”

“…Chemical compounds with 1,4‐benzoquinone moiety exhibit prominent anticancer, 1–4 anti‐inflammatory, 5 and antimicrobial activity 6 . 2,3‐Substituted benzoquinones have two different reaction centers, therefore, we should expect the differences in the regio‐ and stereoselectivity of the Diels–Alder reaction 7,8 . Monoadducts of various dienes with 1,4‐benzoquinone are usually formed much easier than the subsequent bisadducts.…”

“…6 2,3-Substituted benzoquinones have two different reaction centers, therefore, we should expect the differences in the regio-and stereoselectivity of the Diels-Alder reaction. 7,8 Monoadducts of various dienes with 1,4benzoquinone are usually formed much easier than the subsequent bisadducts. It was noted that the reaction rates of 1,4benzoquinone with dienes are low, and the reaction products are thermally unstable.…”