C-H Activating Carboxylation of Terminal Alkynes with CO2 and Its Application in Synthesis

Yugen Zhang, Dingyi Yu, Siti Nurhanna Riduan, and Jackie Y. Ying

Institute of Bioengineering and Nanotechnology

31 Biopolis Way, The Nanos, Singapore 138669, Singapore

E-mail: ygzhang@ibn.a-star.edu.sg

Carbon dioxide (CO₂) is a non-toxic, non-combustible, non-flammable gas. The use of carbon dioxide as a renewable and environmentally friendly source of carbon in organic synthesis is a highly attractive approach, but its real world application remains a great challenge. The major obstacles for commercialization of most current protocols are their poor catalytic performance and harsh, severe reaction conditions. It is important to develop new reactions and new protocols for CO₂ transformations at mild conditions and in a cost-efficient manner. This presentation will discuss a new way for transforming CO₂ to carboxylic acid through C-H bond activation of terminal alkynes (Scheme 1). Various propiolic acids have been synthesized in good to excellent yields under ambient conditions without consumption of any organometallic or organic reagent additives. Different approaches have been developed for this transformation. A copper-catalyzed and copper-N-heterocyclic carbene co-catalyzed C-H activating carboxylation of terminal alkynes with CO₂ has led to the formation of propiolic acids at ambient conditions. A transition metal-free system and a recyclable heterogeneous catalyst system have also been developed for this reaction. Furthermore, the application of this reaction in the stereoselective coupling of terminal alkynes and thiols under carbon dioxide atmosphere will be presented (Scheme 2).

Scheme 1

                                      Scheme 2

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American Institute of Chemical Engineers Annual Meeting, Symposium on 'Chemical Production from CO₂,' TDB03, Pittsburgh, Pennsylvania, USA, October 28‒November 2, 2012.