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

N-2-Sulfonyl-alpha-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 alpha,beta-unsaturated amidines in high yield and with excellent Z-selectivity.

Automated summary

N-2-Sulfonyl-alpha-diazo amidines can be synthesized through the 1,3-dipolar cycloaddition reaction with excellent regioselectivity. The use of electron poor nitrobenzenesulfonyl group and large carboxylate rhodium ligands allows for controlling the outcome and selecting for 1,2-H shift, resulting in high yielding and excellent Z-selectivity of alpha,beta-unsaturated amidines.