Dissection of stereoelectronic effects in the transition states (TSs) for noncatalyzed azide– alkyne cycloadditions suggests two approaches to selective transition state stabilization in this reaction. First, the formation of both 1, 4-and 1, 5-isomers is facilitated via hyperconjugative assistance to alkyne bending and C··· N bond formation provided by antiperiplanar σ-acceptors at the propargylic carbons. In addition, the 1, 5-TS can be ...
