The Synthesis of 3-Substituted Pyrroles from Pyrrole

Pyrrole is a "π-excessive" heteroaromatic that electrophiles substitute preferentially in the 1- or 2-position, making the synthesis of 3-substituted pyrroles very difficult. New procedures are available whereby 3-substituted pyrroles may be prepared in synthetically useful amounts in two or three steps from pyrrole. Initially substituents are introduced onto the 1- or 2-position of the pyrrole ring, which then direct further substitution to a β-position or which may themselves be rearranged to the desired 3-substituted pyrroles. A final step removes any remaining undesired substituents. 1. Introduction 2. Direction by a Removable 2-Substituent 3. Direction by a Removable 1-Substituent 4. Group Migration to Position-3 5. Directed Metallation to Position-3