[harami]

I understand the endo rule and what contributes to the stereochemistry there, it is the diene that confuses me. I know that cis produces the same side substituents (pointing up or down) and trans pointing down or up. Is there any preference towards which points in what direction?

For example, if you have a cis, how do you know if they both point up or down, or would you get enantiomers where one has both pointing up, and both has both pointing down?

[movies]

Could you draw what you mean?  There are two alkenes in the diene, so you have to think about the geometry of both of them, so saying the "cis diene" doesn't really mean anything....

[ch3m_boy]

I got a diff kind of stereochem question.

Basically, in general, if my teacher asks what are the major products of some reaction,

1.)  If the reagents and conditions are not stereoselective, will there always exactly 4 or 3 products, 2 enatiomers for the syn addition and 2 for the anti additon, or if one of the molecules is meso, there will only be 3..  Is that true???

[movies]

For the Diels-Alder reaction you would expect to see two sets of racemic diastereomers, four stereoisomers in total.  More are possible in some cases where the dienophile and the diene are not symmetric because you could have "head-to-head" and "head-to-tail" orientations.  In that case I think you could get 8 stereoisomers.

You're right that for each meso diastereomer you will have one fewer total stereoisomers.  Note that in the D-A of cyclopentadiene and maleic anhydride, there are only two possible stereoisomers, then endo and exo, both of which are meso.