Unexpected rearrangements of rhodium carbenoids containing a pyrrolidin-1-yl group

Ketone- and ester-substituted diazo compounds, which contain a pyrrolidine moiety were treated with dirhodium tetraacetate generating the corresponding rhodium carbenoids. They were expected to insert into a CH bond of the pyrrolidine moiety but reacted differently. The ketone-substituted rhodium carbenoid underwent a Wolff rearrangement. The resulting ketene continued to react by lactamization and electrocyclic ring-opening and gave an acrylamide. The ester-substituted rhodium carbenoid underwent a [1.2]-shift of the (pyrrolidin-1-yl)methyl moiety, which resulted in a methacrylic ester. For each rearrangement a mechanism is suggested.