What are Diels Alder reactions used for?
They are a very common synthetic organic mechanisms for making ring compounds.
The Diels-Alder reaction combines a diene (a molecule with two alternating double bonds) and a dienophile (an alkene) to make rings and bicyclic compounds.
The three double bonds in the two starting materials are converted into two new single bonds and one new double bond. Since this reaction forms two new carbon-carbon bonds in a single step, it is a very useful and powerful reaction (one which earned Otto Diels and Kurt Alder a Nobel prize in chemistry in 1950 for discovering it). http://www.chemhelper.com/dielsalder.html