Experimental and semiempirical studies of effect of MCM-41 and cation exchanged zeolite Y on rate enhancement and diastereoselectivity of Diels–Alder reaction of p-benzoquinone and some derivatives with cyclopentadiene

The MCM-41 and zeolite Y exchanged with Li+, Na+, K+ and Cs+ were used as catalyst for Diels–Alder reaction of cyclopentadiene (CPD) with p-benzoquinone (PBQ) and some derivatives to achieve higher reaction rate and diastereoselectivity. The 2:1 CPD–PBQ adducts of endo-anti-endo and endo-anti-exo obtained, respectively, in the case of PBQ as the major product in the presencece of MCM-41 and CsY is remarkable. Semiempirical calculation by PM5 method was carried out to define the energetics of the system and Goering–Schewene diagram under the catalytic effect of BF3 and AlCl3 Lewis acids. It was found that even though the endo-anti-exo is thermodynamically more stable than endo-anti-endo in uncaytalyzed Diels–Alder reaction, the latter is the more stable isomer in the presence of Lewis acid catalyst.

The 2:1 adducts of Diels–Alder reaction of cyclopentadiene with p-benzoquinone catalyzed by MCM-41 and alkali cation exchanged zeolite Y characterized as endo-anti-endo and endo-anti-exo as the major products, respectively, were rationalized by semiempirical calculations using PM5 method. Figure optionsDownload as PowerPoint slide