Ring Expansion and Rearrangements of Rhodium(II) Azavinyl Carbenes

The ring expansion and rearrangement of diazo compounds, specifically rhodium carbenes (derived from the corresponding diazo species), is an efficient and operationally simple method for the construction of structurally unique frameworks.[ 1] Products derived from these reactions normally consist of large carbocyclic rings (7, 8, and 9 membered) and multiple substituted olefins, which are ubiquitous in natural products and drug molecules.[2] Indeed, these robust methods have found widespread use in organic synthesis, both for the synthesis of complex natural products and in pharmaceutical research.[3] Bolstered by our recent success utilizing readily available and stable 1-sulfonyl-1,2,3-triazoles 1 as direct precursors to rhodium(II) azavinyl carbenes 2 (Scheme 1),[4,5] we hypothesized that these diazo progenitors could be effective in these ring expansion/rearrangement reactions, to deliver unique products that are not accessible via conventional diazo compounds (Scheme 2). Herein, we report the rhodium(II)-catalyzed ring-expansion and rearrangement reactions of azavinyl carbenes (2), to access various enaminones and substituted olefins, which, in the case of the expanded enaminones can be further reacted to form a variety of heterocycles and ketone-based products. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.