Development of a Nazarov Cyclization/Wagner−Meerwein Rearrangement Sequence for the Stereoselective Synthesis of Spirocycles

A stereoselective Nazarov cyclization/Wagner−Meerwein rearrangement sequence for the synthesis of spirocyclic compounds was developed. While a range of different substrate types engaged in the cyclization/rearrangement sequence, it was found that different substrates underwent different reaction pathways. Depending on the substitution pattern of the substrate, the sequence was terminated by either a hydride shift or the shift of a vinyl or aryl group. It was also possible to install adjacent quaternary stereocenters using this protocol. The efficiency of the Wagner−Meerwein rearrangement was found to be dependent upon both the type and the amount of promoter used to generate the intermediate oxyallyl cation.