Organocatalytic [4+2] addition reactions via tetraenamine intermediate†
The [4+2]-cycloaddition reaction of 3-olefinic oxindoles with a tetraenamine intermediate is presented. In the reaction, a novel class of highly functionalized spirocyclic cyclohexanes with four stereocenters is formed in high yield and excellent stereoselectivity. Mechanistic investigations and calculations point to a stepwise mechanism involving tetraenamine intermediates. Furthermore, several transformations are presented.