N. Choony et al., ON THE USE OF REMOVABLE STERIC BUTTRESSES IN CYCLOADDITION REACTIONS, Journal of the Chemical Society. Perkin transactions. I (Print), (13), 1998, pp. 2017-2021
Use of bulky protecting groups, such as the trityl group, can be utili
sed to encourage cycloaddition reactions that otherwise do not proceed
. Thus N-allylfurfurylamines, bearing the appropriate N-protecting gro
up, can thermally cyclise; subsequent removal of the protecting group
produces the thermodynamically unstable, free amine.