50 Years of Zweifel Olefination: A Transition-Metal-Free Coupling

The Zweifel olefination is a powerful method for the stereoselective synthesis of alkenes. The reaction proceeds in the absence of a transition-metal catalyst, instead taking place by iodination of vinyl boronate complexes. Pioneering studies into this reaction were reported in 1967 and this short review summarizes developments in the field over the past 50 years. An account of how the Zweifel olefination was modified to enable the coupling of robust and air-stable boronic esters is presented followed by a summary of current state of the art developments in the field, including stereodivergent olefination and alkynylation. Finally, selected applications of the Zweifel olefination in target-oriented synthesis are reviewed. 1 Introduction 2.1 Zweifel Olefination of Vinyl Boranes 2.2 Zweifel Olefination of Vinyl Borinic Esters 2.3 Extension to Boronic Esters 3.1 Introduction of an Unsubstituted Vinyl Group 3.2 Coupling of α-Substituted Vinyl Partners 3.3 Syn Elimination 4 Zweifel Olefination in Natural Product Synthesis 5 Conclusions and Outlook.