2- and 3-Vinylindoles as 4π Components in Cycloaddition Reactions

The review summarizes the most recent achievements in the chemistry of 2-vinylindoles and 3-vinylindoles. In particular, we focus on the behavior of these compounds as dienes in cycloaddition reactions. The majority of the literature in this field deals with [4+2] cycloaddition, and only one report of [4+1] cycloaddition has appeared in the literature until now. Thus, the main section reviews [4+2] cycloaddition with activated cyclic and acyclic dienophiles under Lewis-acid catalysis or organocatalysis conditions. In addition, cycloadditions performed with simple π-systems as dienophiles, occurring through activation by transition-metal catalysts, are reviewed. This section mainly involves the use of allenes as dienophiles under gold catalysis conditions. In both cases, the authors report excellent levels of diastereoselectivity and enantioselectivity. Two separate subsections deal with the synthesis of natural compounds and with the use of methyleneindolinones as dienophiles.