The N-cyclopropylimine-1-pyrroline photorearrangement as a synthetic tool: scope and limitations.

The scope and limitations of the photorearrangement of N-cyclopropylimines to 1-pyrrolines are presented. The influence on the reactivity of different substituents throughout the cyclopropane ring and at the iminic position of the N-cyclopropylimine structure is discussed. The observed effects are interpreted from computational studies. The principal findings relate to (1) the enhanced reactivity of 1-substituted compounds toward rearrangement, (2) the lack of reactivity of crowded cyclopropanes, and (3) the high chemoselectivity of the process.