I am writing a synthesis proposal to make the compound 4 in the reaction scheme attached.
Notice the stereochemistry; the hydrogen atoms in the middle bond (between the two rings) are
both pointing downward.
I was planning to make 4 via an intramolecular Diels-Alder reaction in compound 3.
I would expect that the hydrogens can end up on either side of the plane; either both pointing upward (undesired),
or both pointing downward (desired), so a mixture of both is obtained.
Would anyone have a suggestion for me on how to ensure the hydrogens are both pointing downward?