Liu X, Ma X, Huang Y, Gu Z * University of Science and Technology of China, Hefei, P. R. of China
Pd-Catalyzed Heck-Type Cascade Reactions with
N-Tosyl Hydrazones: An Efficient Way to Alkenes via in Situ Generated Alkylpalladium.
Org. Lett. 2013;
15: 4814-4617
Key words
palladium - Heck reaction -
N-tosyl hydrazones
Significance
Palladium-catalyzed Heck-type cascades have long been used to install molecular complexity in a single transformation. In early pioneering work, Negishi and Grigg have reported cascade processes involving carbonylation sequences, Stille and Suzuki couplings, as well as C−H functionalization as terminating steps. However, despite these advances, terminations involving palladium carbenes have been far less explored. Gu and co-workers report the combination of N-tosyl hydrazone derived carbenes and in situ generated alkyl palladiums in a new alkenylation reaction.
Comment
The authors present a palladium-catalyzed Heck-type cascade reaction en route to alkene products. By terminating the cyclization sequence with a reaction with N-tosyl hydrazones, products can be obtained with high E/Z ratios. The method benefits from the ability to generate diverse hetero- and carbocycles in good to excellent yields under relatively mild conditions, using a simple palladium(II) pre-catalyst. Cyclization onto electron-deficient alkenes was shown to be preferred in a competition experiment involving a diene substrate.
