It is said that the Diels-Alder reaction is a syn-addition with respect to both the dienophile and the diene. Is there a reason for that!?
1 Answer
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https://www.nyu.edu/classes/tuckerman/adv.chem/lectures/lecture_17/node8.html
Of course there is a reason.
Interaction of these HOMO and LUMO is only possible as in the image, in a certain alignment which results in syn addition product.