Controlling Selectivity in the Synthesis of Z‐α,β‐Unsaturated Amidines by Tuning the N‐Sulfonyl Group in a Rhodium(II) Catalyzed 1,2‐H Shift

Abstract N 2 ‐Sulfonyl‐α‐diazo amidines can be synthesized by the reaction of electron rich alkynyl amines with electron poor sulfonyl azides through 1,3‐dipolar cycloaddition that proceeds with perfect regioselectivity. In the presence of rhodium(II) carboxylate catalysts, denitrogenation occurs to give the corresponding metallocarbene but there are then two competing processes: 1,2–H shift and O ‐transfer from the sulfonyl group to the metallocarbene center. The outcome can be controlled using an electron poor nitrobenzenesulfonyl group and large carboxylate rhodium ligands to select for 1,2–H shift, forming α,β‐unsaturated amidines in high yield and with excellent Z‐selectivity.