Thermal Cycloadditions

Abstract

We dealt with [4+2]-cycloadditions very briefly in Section 3.3.1. As you saw there, a [4+2]-cycloaddition requires two different substrates: one of these is an alkene—or an alkyne—and the other is 1,3-butadiene or a derivative thereof. The reaction product, in this context also called the cycloadduct, is a six-membered ring with one or two double bonds. Some hetero analogs of alkenes, alkynes, and 1,3-butadiene also undergo analogous [4+2]-cycloadditions. In a [2+2]-cycloaddition an alkene or an alkyne reacts with ethene or an ethene derivative to form a four-membered ring. Again, hetero analogs may be substrates in these cycloadditions; allenes and some heterocumulenes also are suitable substrates.