Wolff rearrangement protocols

The requisite a-diazo thiol esters are conveniently prepared by using the "detrifluoroacetylative" diazo transfer strategy previously developed in our laboratory. Cycloadditions are best carried out by using as little as 0.006 equiv of rhodium(II) acetate to promote the thia-Wolff rearrangement. Reactions involving the more nucleophilic ketenophiles proceed smoothly in refluxing dichloromethane (40°C), while cycloadditions with less reactive partners are best accomplished in 1,2-dichloroethane (83°C). As is standard for ketene cycloadditions, the optimal protocol involves slowly adding a solution of the diazo thiol ester to a solution of the ketenophile and catalyst in order to minimize competitive ketene dimerization. 

An alternative synthetic approach to obtain cyclic enaminones from bromodiazoacetone 291, primary amines, and alkynes is based on a sequential aza-Michael addition/Wolff rearrangement, and nucleophihc ketene cyclization which was performed in a one pot fashion has been reported (Scheme 93) (20110L2147). Using this protocol, a collection ofenaminone reaction products 292—297 was obtained in satisfactory yields (Scheme 93). 

The microwave-assisted Wolff rearrangement of cyclic 2-diazo-l,3-diketones was performed in the presence of a stoichiometric amount of alcohol, amine, or thiol (Presset et al., 2009b). It is an efficient, and environmentally friendly synthetic protocol for the synthesis of a-earbonylated cycloalkanones. This approach proves superior to existing protocols in scope and ecocompatibility. 

---