When 1, 3-cyclopentadiene and maleic anhydride (Eq. 15.12a, p.698) are allowed to react at room temperature, a Diels-Alder reaction takes place in which the endo product is formed as the major product. When this product is heated above its melting point of 165oC, it is transformed into an equilibrium mixture that contains about 57Vo of the exo stereoisomer and 43Vo of the endo stereoisomer. (The equilibrium constant for inter-conversion of the two stereoisomers probably does not vary greatly with temperature.)
Eq. 15.12a

(a) Show these transformations with equations, including the structures of all compounds.
(b) According to these observations, is the Diels-Alder reaction of maleic anhydride and 1, 3-cyclopentadiene at room temperature a kinetically controlled or a thermodynamically controlled reaction?
(c) Draw two diagrams like Fig. 15.8, p. 695, one showing the transition state that leads to the endo product, and the other showing the transition state that leads to the exo product. According to the data in this problem, which diagram portrays the transition state of the reaction at low temperature?
Fig. 15.8

Transcribed Image Text:

H,C_C_-С-С C_CH, + maleic anhydride (Ecl. 15. 12a, p. 698) -- dienophile overlap of 2p orbitals to form a new orboned overlap of 2p orbitals to form a new or bond diene