The diene 16-DPA addition reaction is a cycloaddition reaction of a conjugated diene system with an alkene or alkyne bond to obtain a cyclohexene or 1,4-cyclohexadiene ring system. In 1928, German chemists OPH Diels and K. Alder discovered this type of reaction when studying the interaction of butadiene and maleic anhydride: In this type of reaction, the ene and alkyne that interact with conjugated dienes are called affinity Diene body. The electron-withdrawing substituents on the dienophile (such as carbonyl, cyano, nitro, carboxyl, etc.) and the electron-donating substituents on the conjugated dienes have the effect of accelerating the reaction.

This type of reaction has strong regional and stereoselectivity. When both the diene and the dienophile have appropriate substituents, so that the reaction may occur in different locations to obtain two products, in fact only one is the main one. For example, isoprene reacts with butenone to obtain methyl-(4-methyl-3-cyclohexenyl, 16-DPA)-methanone: in terms of stereochemistry, these reactions are all cis Formula is additive, and when the reactants are likely to produce both internal and external products, generally only internal compounds, such as the reaction of cyclopentadiene and maleic anhydride:

These stereoselectivity not only conform to a large number of experimental facts, but also can be explained theoretically by the principle of conservation of molecular orbital symmetry.

Diene addition reactions are generally reversible, and this reversibility is sometimes well applied in synthesis. 16-DPA, for example, when a small amount of butadiene is used in the laboratory, it can be obtained by pyrolyzing cyclohexene. The synthesis of methyl 2-cyclopropenyl formate also utilizes Diels-Alder reaction and its reverse reaction.