Near-simultaneous reports of an interesting new pyrrole (and dihydropyrrole) synthesis have appeared recently from the labs of Frank Glorius (Westfälische Wilhelms-Universität Münster) and Naohiko Yoshikai (Nanyang Technologial University, Singapore).  Optimization of the additives, solvent, and temperature led to essentially the same conditions from each laboratory.  A balloon of oxygen is preferred: yields are much lower when air is used.  A Heck-type mechanism is shown, but a Wacker-type mechanism involving nucleophilic attack of an enamine onto a Pd-complexed alkene could not be ruled out.

The scope of the reaction is decent, as indicated below.  Failures include R₃ = CF₃ or cyclopropyl and R₂ = Ph.  N-Homoallylic and N-cinnamyl imines were also unsuccessful.

Specific examples are shown below: