[Diversification of Unsaturated Hydrocarbons via An Azo-Ene Reaction]

Unsaturated hydrocarbons represent one of the most abundant and synthetically versatile classes of organic molecules. Consequently, the development of new strategies to enable their facile transformation into value-added molecules is a longstanding goal in modern organic chemistry. In this review, we summarize our recent progress in the diversification of simple unsaturated hydrocarbons via ene reactions with 1,2,4-triazoline-3,5-diones (TADs), a highly reactive class of azo compounds. A key breakthrough involved the use of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the solvent, which significantly facilitates otherwise sluggish azo-ene reactions. The resulting TAD-ene adducts-presumably generated through a stepwise pathway-underwent diverse downstream functionalizations, including reactions with Grignard reagents and transition metal catalysts, to access structurally and functionally complex products. Notably, HFIP also promotes an unusual [3+2] cycloaddition between TADs and alkynes, leading to the discovery of unprecedented mesoionic compounds-five-membered heterocycles that cannot be represented satisfactorily by any one covalent or polar structure.