Highly <i>Z-</i>Selective Julia–KocienskiOlefination Using <i>N</i>‑Sulfonylimines and ItsMechanistic Insightsfrom DFT Calculations

The Julia–Kocienski (JK) olefination is effective for <i>E</i>-selective olefination, but highly <i>Z</i>-selective versions remain rare. Here, we report a highly <i>Z</i>-selective JK olefination (<i>Z</i> ratio >99:1) using <i>N</i>-sulfonylimines as electrophiles instead of aldehydes. This method demonstrates a broad substrate scope, tolerating electron-donating and -withdrawing groups, amides, halogens, carboxylic acids, and hydroxyls. <i>Z</i>-selectivity in our system arises from both the 1,2-addition and Smiles rearrangement steps without involving synperiplanar elimination. This study expands the toolkit for <i>Z</i>-selective olefin synthesis.