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

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.…”

“…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. The molecule 5 is symmetric (C s ) and has a plane of symmetry passing perpendicular to the directions to the carbonyl groups through the middle of the central six-membered cycle (projection c, Figure 2).…”

“…The endo structure of adducts (3) and (4) has been proven previously. 7,8 A huge difference in the rates of reaction 1+2→3 and 1+4→5 with the participation of activated C 2 =C 3 bonds (k 1 /k 2 = 515; issues 1 and 3, Table 1), as well as with the participation of non-activated bonds (k 1 /k 2 = 187; issues 11 and 12, Table 1) indicates great steric difficulties in the formation of a transition state with a parallel arrangement of diene (1) and monoadducts. The data obtained (Tables 1 and 2) make it possible to calculate activation enthalpies for the decomposition reactions of the bisadduct 5→1+3 (99 kJ mol −1 ) and 5→1+4 (81 kJ mol −1 ).…”

“…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.…”