Alexandria Digital Research Library

I. Suzuki-Miyaura Cross-Couplings in Water Facilitated by Nonionic Amphiphiles II. Room Temperature C-H Activation Catalyzed by Cationic Palladium

Abela, Alexander
Degree Grantor:
University of California, Santa Barbara.Chemistry
Degree Supervisor:
Lipshutz Bruce H
Place of Publication:
[Santa Barbara, Calif.]
University of California, Santa Barbara
Creation Date:
Issued Date:
Organic chemistry
green chemistry
C-H Activation

Palladium-catalyzed cross-couplings have emerged as one of the most efficient approaches to carbon-carbon bond formation in modern organic chemistry. Even with several decades of study, however, a variety of avenues for improvement in terms of reaction scope and both environmental and synthetic efficiency remain.

Among the most widely used transformations in this class is the Suzuki-Miyaura cross-coupling of halides or pseudohalides and boronic acid derivatives. Although these reactions are primarily carried out in wet organic solvent, use of water alone as a reaction medium yields a number of advantages in terms of cost, safety, and minimization of organic waste. Small amounts of nanomicelle-forming nonanionic amphiphiles were found to facilitate efficient Suzuki-Miyaura couplings in water, usually at room temperature. A variety of challenging substrate classes were found to be amenable to these conditions, including electron-rich aryl chlorides, pseudohalides, and highly lipophilic substrates. The conditions have been further extended to include valuable heteroaryl halides and boronic acids as coupling partners.

With the additional promise of increased synthetic efficiency that it provides, the direct fuctionalization of carbon-hydrogen bonds through transition metal-catalyzed "C-H activation" chemistry has recently generated considerable interest. Previously reported conditions to achieve direct reactions at aromatic C-H positions have generally required harsh conditions, including high temperatures to achieve direct reactions at these positions, often resulting in limitations in substrate scope and selectivity. Cationic palladium catalysts were found to be highly active in promoting C-H activation reactions of aryl ureas at ambient temperatures, leading to some of the mildest conditions yet reported for transformations in this class. Room temperature ortho-arylations were carried out using aryl iodides in water, while aryl boronic acids could be coupled in EtOAc, also at ambient temperatures. Conditions for room temperature Fujiwara-Moritani couplings between aryl ureas and acrylate derivatives were also developed. Studies aimed at better understanding the reaction conditions and mechanism were conducted, and a possible palladacycle intermediate was isolated and characterized by X-ray crystallography.

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