The nucleophilic substitution has been widely used to create strained rings, but the synthesis of functionalized precursors is an open issue. For instance, lengthy linear sequences were used to prepare the relatively simple a-vinyl azetidine, 3e,f which is a highly versatile species (Scheme 1b). Elegant catalytic methods based on the release of ring strain have been presented. 5 N-protected azetidines can be accessed from b-iodo ynamides. These approaches require however the presence of sacrificial groups. Higher atom-economy has been achieved by few Energy-Transfer (EnT) methods. A strain-release approach uses [1.1.0]-azabicyclobutanes and a N-sulfonyl diarylimine. An intermolecular [2+2] photocycloaddition combines a b-carboxy oxime with a styryl fragment. Sensitized aryl-methacrylamides can deliver b-lactams via hydrogen-atom-transfer (HAT) to an alkyl radical. 11 So-far, EnT strategies were focused on the activation of conjugated pbonds, and the required auxochromes, such as aryl-rings and carbonyl groups (Scheme 1c, highlighted in orange), limit the chemical space that can be accessed by these methodologies.