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Rank the following dienes in order of decreasing reactivity with a dienophile in a Diels-Alder reaction. (1 = most reactive).
To undergo a Diels-Alder reaction, a dienophile must be in s-cis conformation.
The bicylic compound below is locked into s-trans conformation; it can never rotate into s-cis conformation and so can't undergo a Diels-Alder reaction.
Of the other two compounds, the middle compound most easily rotates into s-cis conformation, and so will undergo a Diels-Alder reaction the fastest. The compound on the right has steric strain when in s-cis conformation, and so won't do Diels-Alder as easily.
Predict the product for each Diels-Alder reaction. Indicate stereochemistry where appropriate.
When approaching Diels-Alder problems, it's always good to user numbering: the product is always a cyclohexene compound.
In b), the trans dienophile leads to a trans product.
In c), the dienophile is an alkyne, and so becomes an alkene in the product.
Chair forms can be difficult to draw, so it's a good diea to draw the "overhead view" first.
Retro Diels-Alder: show a combination of diene and dienophile that would result in each Diels-Alder adduct.
When in doubt, use numbering.
Since chair forms can be cumbersome to deal with, always convert them to plain "overhead view" structures before doing the problem.
