Investigating a dearomatising, thionium ion azaspirocyclisation

Electron rich N-benzyl glyoxamides bearing at least two ipso-directing groups can be converted into 2-[4.5]-azaspirocyclic cyclohexadienones upon treatment with a thiol, trifluoroacetic anhydride and BF₃-OEt₂, via a dearomatising, thionium ion azaspirocyclisation. A modest preference for the anti-diastereoisomer is commonly displayed. In certain cases, the anti-diastereoisomer is the only isomer formed. Notably the cyclisation is not accompanied by competing isoquinolone formation. The sulfanyl group that is introduced upon spirocyclisation can act as a synthetic handle and a stereocontrol element during manipulations of the framework. A range of oxidative and reductive transformations have been explored. In cases where the spirocyclic cationic intermediate is unstable intramolecular aryl transfer and iminium ion hydrolysis furnishes a-aryl acetamides. Selective C-alkylation and desulfurisation provides a means of accessing functionalised α-aryl acetamides.EThOS - Electronic Theses Online ServiceGBUnited Kingdo