Addition Reactions: Cycloaddition

The enantioselective N-heterocyclic carbene-catalysed formal 2+2- and 2+2+2- cycloadditions of ketenes with isothiocyanates can be investigated. At room temperature, the reaction of N-arylthiocyanates favours the 2+2-cycloaddition. However, at −40°C, N-benzoylisothiocyanates undergo the 2+2+2-cycloaddition. This chapter discusses cycloaddition-type addition reactions. Specifically, it covers three types of cycloadditions: 2+2-cycloaddition, 2+3-cycloaddition and 2+4-cycloaddition. Miscellaneous cycloaddition reactions are separately described at the end of the chapter.