Iminyls. Part 5. Intramolecular hydrogen abstraction by alkyl(aryl)iminyls. A new tetralone synthesis

Abstract

Tetralones can be synthesised by oxidation of phenylalkylideneamino-oxyacetic acids with persulphate. The iminyls formed initially abstract a y-hydrogen from the alkyl chain and the resulting carbon radicals then cyclise onto the benzene ring. The same iminyls, when generated in benzene solution by thermolysis of imino-oxyperacetates, do not abstract y-hydrogen unless trifluoroacetic acid is present. Hence, the hydrogen abstracting species in both cases is thought to be the protonated iminyl (RArC=NH).

Photoinduced Remote Functionalisations by Iminyl Radical Promoted C−C and C−H Bond Cleavage Cascades

“…A polarity‐matched S H 2 reaction with a SOMOphile (to give I ) and hydrolysis would provide the γ‐functionalised ketone J , which would be unreactive under classical ionic reaction conditions. We were, however, concerned by the fact that 1) 1,5‐hydrogen abstractions involving iminyl radicals are known to require acidic conditions,, which would not allow for decarboxylation in our system, and that 2) radical H is prone to undergo intramolecular cyclisation when R=aromatic as reported by Forrester and Nevado ,,…”

Iron‐Catalysed Remote C(sp3)−H Azidation of O‐Acyl Oximes and N‐Acyloxy Imidates Enabled by 1,5‐Hydrogen Atom Transfer of Iminyl and Imidate Radicals: Synthesis of γ‐Azido Ketones and β‐Azido Alcohols

“…Performing the reaction in anhydrous solvent afforded a significant amount of the aza‐diene 7 (Scheme b), probably resulting from the dimerisation of the γ‐azido imine 8 , which was also observed in the 1 H NMR spectrum of the crude product. In practise, commercially available t BuOH was the best reaction media; 4) Adding one equivalent of acetic acid (HOAc) to the reaction mixture increased the yield of 3 a and accelerated the reaction, probably by speeding up the 1,5‐HAT process . Overall, performing the reaction of 2 a with TMSN 3 (3.0 equiv) in t BuOH ( c 0.05 m ) in the presence of AcOH (1.0 equiv) and Fe(acac) 3 (0.2 equiv) at 50 °C afforded the azido ketone 3 a in 89 % isolated yield.…”

Visible‐Light‐Mediated Remote Aliphatic C−H Functionalizations through a 1,5‐Hydrogen Transfer Cascade

“…To the best of our knowledge, only a handful of examples have showcased 1,5‐HAT in an iminyl radical . In fact, as reported by Forrester et al., a subsequent C−C bond formation can then occur. However, the strongly oxidizing conditions, elevated temperatures, low yields of the product and narrow substrate scope have hampered synthetic applications of these protocols.…”