α‐Hydrogen spirocyclic alkoxyamines synthesis: ESR verified Nitroxides generation and their potential application in NMP polymerization

Abstract

AbstractHerein, we report a synthetic methodology towards the construction of new cylic alkoxyamines without the prior obtention of their respective nitroxides. These systems are constituted by an indene core connected to a pyrrolidine nucleus through a spiro carbon atom, containing an adjacent α‐hydrogen to the N atom, in order to exhibit the 1‐azaspiro[4.4]nonane frame. Alkoxyamines were synthesised by a free radical‐based spirocyclization, starting from functionalized oxime ethers, involving aryl and neutral alkoxyaminyl radicals in 16–40 % yields. Then, the novel spirocyclic aminoxyl radicals (nitroxides) were detected in ESR spectra, when alkoxyamines were subjected by the thermal homolytic cleavage of their −C−O−N− bond. In general, the temperatures found were in accordance with the increase in the stability of the carbon‐centred radical for the same type of nitroxides. In addition, a spirocyclic alkoxyamine 8 b with α‐hydrogen was employed as initiators/mediators in the styrene bulk homopolymerization, obtaining high conversions and relatively narrow dispersity (Ð~1.5). This suggests that the synthetic methodology used in this research work to obtain α‐hydrogen spirocyclic alkoxyamines would have the potential to be applied in nitroxide‐mediated polymerization (NMP).