5 - Max-Planck-Institut für Kohlenforschung

48
Synthetic Organic Chemistry – L. J. Gooßen
2.1.8 Research Area "New Transition Metal-Catalyzed Reactions
Involved: J. Paetzold, D. Koley
for Organic Synthesis" (L. J. Gooßen)
Objective: Our research is devoted to the development of transition metal-catalyzed
reactions for organic synthesis. New processes were discovered for the preparation of
important classes of compounds which had previously been accessible only over
numerous steps or with the use of sensitive, aggressive or toxic reagents. Key
characteristics of all these new procedures are their excellent practicability and
tolerance of functional groups.
Results: Within the last two years, we focused on the development of cross-coupling
reactions where the substrates are carboxylic acids instead of the ecologically
questionable acyl or aryl halides usually used (Scheme 1). The carboxylic acids were
activated in situ with coupling reagents, to allow an oxidative addition to transition
metal catalysts.
R
R Ar
R"
R'
- CO
Ar-
- CO
B(OH) 2
- H 2 O
- CO
R' Na H2PO2
O
+
R OH +
coupling
reagent
cat.
Scheme 1. Reactions of carboxylic acids
Ar- B(OH) 2
R'OH
O
R H
O
R Ar
O
R O
This approach led to the discovery of a selective catalytic transfer hydrogenation of
carboxylic acids to aldehydes. The acids are converted in situ into anhydrides using
pivalic anhydride, and consequently reduced with sodium hypophosphite in the
presence of a palladium catalyst.
The same principle was utilized in our new ketone synthesis, in which carboxylic acids
are coupled with boronic acids. Three reaction variants were developed, with the
activating agents pivalic anhydride, dimethyl dicarbonate and disuccinimidyl carbonate.
This reaction is the first to give convenient access to a number of functional ketones
directly from the corresponding carboxylic acids.
Acyl-palladium complexes decarbonylate at elevated temperatures. This behavior was
exploited in a new decarbonylative Heck olefination of carboxylic acids. In this process,
R'