Combination of Rearrangement with Metallic and Organic Catalyses - a Step- and Atom-Economical Approach to α-Spirolactones and -lactams

A general synthetic route to alpha-spirolactones and -lactams from 2-diazo-1,3-dicarbonyl compounds, (homo)allylic alcohols or amines and acrylic dertivatives, involving a single consecutive reaction consisting of a Wolff rearrangement/alpha-oxo ketene trapping/cross metathesis/Michael addition sequence is described. During the consecutive reaction optimization, the organocatalytic activity of N,N-diaryl-1,3-imidazol(in)-2-ylidene N-heterocyclic carbenes (NHCs) in the Michael addition of 1,3-dicarbonyl compounds was discovered. A conceptually attractive version of the consecutive reaction was then developed, involving the Grubbs-Hoveyda ruthenium-based precatalyst containing the SIMes [1,3-bis (2,4, 6 -trimethylphenyl)imidazolin-2-ylidene] NHC ligand as the source of both the organometallic catalyst of the cross metathesis and the organic catalyst of the intramolecular Michael addition.