Chloroform as a Carbon Monoxide Precursor: In or Ex Situ Generation of CO for Pd-Catalyzed Aminocarbonylations

Abstract

Conditions for the rapid hydrolysis of chloroform to carbon monoxide (CO) using heterogeneous CsOH·H2O are described. CO and (13)CO can be generated cleanly and rapidly under mild conditions and can be captured either in or ex situ in palladium-catalyzed aminocarbonylation reactions. Utilizing only 1-3 equiv of CO allows for the aminocarbonylation of aryl, vinyl, and benzyl halides with a wide variety of primary and secondary amines giving amide products in good to excellent yields.

Ligand-free Pd(0)/SiO2-catalyzed aminocarbonylation of aryl iodides to amides under atmospheric CO pressure

“…In the absence of catalyst, no product was obtained. In the case of only using Pd/ SiO 2 without K 2 CO 3 , a small amount of the desired product (10%) was obtained ( supports provided the desired product in moderate to good yields (from 42% to 84%) under similar reaction conditions (entries [11][12][13][14][15][16][17][18]. Therefore, Pd/SiO 2 catalyst was found to be the optimum catalyst for the carbonylation of iodobenzene.…”

Cooperative redox activation for carbon dioxide conversion

“…Its high toxicity and flammability has always been the sticky point in the handling and transportation of this gas, and therefore the identification of viable surrogates is welcomed. Indeed, several research groups have successfully disclosed the suitability of a number of different CO releasing reagents, such as aldehydes, alcohols and acid chlorides, but all have disadvantages with respect to atom efficiency and price567. Carbon dioxide represents another one carbon molecule being highly abundant but compared with CO it displays high kinetic and thermodynamic stability.…”

Palladium‐Catalyzed Aminocarbonylation Reaction to Access 1,3,4‐Oxadiazoles using Chloroform as the Carbon Monoxide Source

“…[12] To the best of our knowledge, there is only one example of an aminocarbonylation reactionu sing chloroform as the CO source. [10] The N-containing heterocycles such as tetrazoles, however, have not been tried yet. Given that 1,3,4-oxadiazoles are of great importance due to their wide applications in pharmaceutical chemistry [13] andm aterial science, [14] andi nc ontinuation of our interest in heterocycles,…”

“…Fort his phenomenon, 31 PNMR spectroscopy and kinetic experiments were undertaken by Hulls group during their experiments. [10] They hypothesized that the active catalyst was generated via oxidation of an equivalent of the ligandt og enerate Xantphos monooxide and Pd(0). Similarly, there are three kinds of different Pd(0) complexes that could exist in the reaction mixture,i ncluding:[ (Xantphos)Pd],[ (Xantphos mono-oxide)Pd],a nd [(Xantphos mono-oxide) 2 Pd].…”

“…Compared with the yield from aliphatic amines such as morpholine,t he lower yield obtained in this reaction systemm ay be attributedt o the relatively lower nucleophilicity of aromatic secondary amines,w hich is consistent with the previous report. [10] With the optimized conditions in hand, as erieso f aryl halides was employed to explore the generality of this protocol( Table2). Generally, all of the investigated aryl halides coupled with 5-phenyl-2H-tetrazole 2a smoothly to provide the 1,3,4-oxadiazolesi nm oderate to good yields (44-75%).…”