Michael−Aldol Ring Closures with Dihapto-Coordinated Pyrrole Complexes and the Synthesis of Tetrahydroindole Cores

Several pyrrole complexes of {TpW(NO)(PMe3)} are evaluated as potential synthons to the indole core. The 2,5-dimethylpyrrole analogue undergoes Michael addition with several enones and enals to form 3H-pyrrole complexes, which subsequently tautomerize and undergo an aldol ring closure to form tetrahydroindole complexes (including one confirmed by crystallographic data). In some cases an organic tetrahydroindole could be recovered, albeit in low yield. Pyrrole N−H insertion was observed for 2-methylpyrrole and 2,4-dimethylpyrrole, and for the latter, a crystal structure is reported for the corresponding seven-coordinate pyrrolyl hydride derived from 2,4-dimethylpyrrole.