This document summarizes work on the Heck reaction and redox-relay Heck reaction. It provides background on the Heck reaction and its applications. It then discusses chain-walking in the Heck reaction where the palladium catalyst migrates down an alkyl chain, producing alkene isomers. It introduces Sigman's work developing a redox-relay Heck reaction where chain-walking of palladium is controlled by an alcohol thermodynamic sink on the substrate, transferring unsaturation to form aldehydes or ketones. It is authored by Margaret Hilton from the Sigman Lab at the University of Utah in 2014.

1. Organic Pedagogical Electronic
Network
Redox Relay Heck Reaction
Margaret Hilton
Sigman Lab
University of Utah
2014

2. Heck Reaction
Review: Chem. Rev. 2000, 100, 3009.
Other Examples and Applications: Overman JACS 1993, 115, 11028 , Sarpong JACS 2008, 130, 7222,
Shibasaki JOC 1996, 61, 4876, Sigman JACS 2010, 132, 13981, Sigman JACS 2011, 133, 9692.
2010 Nobel Prize
*Note: this reaction may also proceed through an oxidative mechanism, where
a PdII precatalyst , a transmetallating aryl reagent, and a terminal oxidant are
used, such as with Heck’s conditions shown.
Since Heck’s seminal publication in 1968,
the Heck reaction has been a powerful
synthetic tool for the functionalization of
olefins with aryl groups.
Heck’s Conditions:
Heck, along with Negishi and Suzuki,
won the Chemistry Nobel Prize in
2010 for their work in cross coupling.
General Mechanism*

3. Chain-Walking
Examples of Relay via Palladium Catalysis
Hayashi JACS 1991, 113, 1417
Curran, JACS 2007, 129, 494
After the initial migratory
insertion, which forms a C-C
bond, a β-hydride elimination
will occur, producing a Pd-H
intermediate. If the alkene
remains coordinated to
palladium and the hydride
reinserts at the opposite carbon,
the palladium catalyst is now
positioned one more carbon
down the alkyl chain. This is
called a “relay” or “chain
walking” and produces alkene
isomers. Can chain-walking be controlled?

4. Redox-Relay Heck Reaction
Sigman Science 2012, 338, 1455
Sigman JACS, 2013, 135, 6830
Classical Variant
Oxidative Variant
Sigman and coworkers have developed a redox-relay Heck reaction, where the relay
by palladium is controlled by a thermodynamic sink (an alcohol) on the substrate. The
unsaturation of the alkene is transferred to the alcohol to form aldehydes or ketones.

5. Problems
1. Keay, JOC, 2007, 72, 7253

6. This work is licensed under a
Creative Commons Attribution-
ShareAlike 4.0 International
License.
Contributed by:
Margaret Hilton
Sigman Lab
University of Utah
2014