I'm familiar with the endo rule as well as the regioselectivity of the reaction. However, what I fail to understand is the stereoselectivity of the product in relation to the diene. For example, in the image below, which one is the correct product? I used to consider only 1 but I've seen several examples, in notes handed by my professor and some books, that provide only 2. enter image description here Also related, which one is accepted from the approachs below? I've seen only 1 being discussed but why should 2 be excluded? From what I've tried, they lead to different products while the orbital rules are not violated. enter image description here

I've seen similar questions with no answers however. Also, books like Clayden's or March's do not point out something similar from what I've seen. The same goes for any website I've checked.

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    $\begingroup$ The two products you drew are enantiomers. In the absence of any chiral catalyst (or other chiral centres in the starting materials), you can only get a racemic mixture of both enantiomers. $\endgroup$ – orthocresol Dec 30 '18 at 1:29
  • $\begingroup$ I see. So in both pictures, both approaches are plausible given the absence of chiral entities? $\endgroup$ – Αντώνιος Κελεσίδης Dec 30 '18 at 8:19
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    $\begingroup$ Yes, not just plausible, but exactly equally plausible, such that you get an exactly 1:1 mixture. $\endgroup$ – orthocresol Dec 30 '18 at 9:30
  • $\begingroup$ When the two achiral entities undergo the DA reaction, two enantiotopic transition states are involved leading to a racemate. The authors presume you are aware of this issue. If they had to draw both enantiomers all the time, your texts would be appreciably more expensive than they already are. ;) $\endgroup$ – user55119 Dec 31 '18 at 0:24

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