Kinetics and thermochemistry of the [2π+2σ+2σ]‐cycloaddition of quadricyclane with 2,3‐dicyano‐1,4‐benzoquinone

Abstract

Two‐stage [2π+2σ+2σ]‐cycloaddition of quadricyclane (2) with 2,3‐dicyano‐1,4‐benzoquinone (1) with a huge difference in the activity of two reaction centers has been studied. In the first stage (kinetic control), the cycloaddition of 2 takes place on the activated С2=С3 bond of 1 to form the monoadduct 3, and in the second stage the cycloaddition of 2 on the С5=С6 bond of the monoadduct 3 occurs by 6 orders of magnitude lower with the formation of bisadduct 4. The structures of adducts 3 and 4 have been proved by NMR data and the X‐Ray method, respectively. The kinetics of the first and second stages, the enthalpy of dissolution of 1 in the π‐donor solvents, and the enthalpy of the reaction 1+2→3 have been measured.

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

“…It was previously shown 14 that among π‐acceptor dienophiles, tetracyanoethylene exhibits the highest selectivity (100%) in the interaction energy with π‐donor solvents, significantly exceeding 2,3‐dicyano‐1,4‐benzoquinone ( 2 ) (64%), 4‐phenyl‐1,2,4‐triazolin‐3,5‐dione (19%), maleic anhydride (15%), and 1,4‐benzoquinone (6%). The tremendous cycloaddition rate of the C 2 ═C 3 bond of dienophile 2 is observed in reactions with quadricyclane (36.9), 9,10‐dimethylanthracene (235), and cyclopentadiene (457 L mol −1 s −1 ; Table 1).…”

“…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 .…”

“…The highest known exothermic heat effect for Diels–Alder reactions is achieved in reaction of quadricyclane ( 6 ) with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( k 25 = 0.282 L mol −1 s −1 , Δ H r‐n = −255.1 kJ mol −1 ) 13 . These parameters were also very high for the addition of quadricyclane ( 6 ) to C 2 ═C 3 bond of 2,3‐dicyanobenzoquinone 2+6→7 : Δ H r‐n = −182.2 kJ mol −1 and k 25 = 36.9 L mol −1 s −1 14 . The exothermicity of the reaction 2+6→7 is noticeably smaller in magnitude compared with the reactions of the quadricyclane with tetracyanoethylene and 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione, but it is still quite high, which makes the reaction 2+6→7 almost irreversible under normal conditions.…”

“…It should be noted that the quadricyclane exhibits an increased rate of [2π+2σ+2σ]‐cycloaddition only with strong electron acceptor dienophiles. So, the rate of reaction 6+7→8 is 6 orders of magnitude lower than that of reaction 2+6→7 14 . This virtually eliminates the possibility of separately determining the kinetic and thermochemical parameters of the reactions by C 2 ═C 3 and C 5 ═C 6 bonds.…”

“…So, the rate of reaction 6+7→8 is 6 orders of magnitude lower than that of reaction 2+6→7. 14 This virtually eliminates the possibility of separately determining the kinetic and thermochemical parameters of the reactions by C 2 =C 3 and C 5 =C 6 bonds. It was found that cyclopentadiene (1) does not show such high rate discrimination with respect to these reaction centers.…”