ABSTRACT
Most of the reactions described in this chapter would fall under Huisgen's definition o f a cycloaddition reaction [1 ]. However, some of the reactions described would not be considered cycloaddition reac tions according to this restrictive definition. Therefore, the more liberal definition given by Baldwin will be used as a guideline, namely,
"Cycloadditions are chemical transformations giving at least one prod uct having at least two new bonds as constitutents o f a new ring" [ 2] . The carbon atoms o f the enamine functional group alone
N
are the sites o f attack and hence provide the two-carbon cyclization bridge in most o f the reactions described, although a few reactions involve an adjacent functional group with the enamine. However, cycloadditions to ternary iminium ions which involve the a-carbon and the nitrogen atom or the carbons o f a cumulated double bond as the sites o f attack are discussed in Chapter 6 (Sections III.C and V ) and will not be discussed here.
