The Synthesis of η²-β-Vinylpyrrole Complexes and Their Conversion to Highly Substituted Indoles

A series of 4,5-η2-Os(II)pentaammine-3-vinylpyrrole complexes are synthesized from the corresponding 1-methylpyrrole complex by an electrophilic addition at the β-carbon, C(3), of the pyrrole ring. Four independent synthetic routes to β-vinylpyrrole complexes are described, each introducing different functionality on the pendant double bond. The uncoordinated portion of these complexes chemically and structurally resembles an aminodiene and as such readily undergoes Diels−Alder reactions with suitably activated dienophiles to generate the 5,6,7,7a-tetrahydroindole nucleus. These tetrahydroindole complexes can be decomplexed and oxidized with DDQ to generate a series of highly functionalized indoles.