Chelation-Assisted Hydroesterification via Ru Catalysis and Bimetallic Coupling Reaction by a Combined Use of Ru and Pd catalyst

Abstract

Part I은 Ru촉매의 catalysis에 의한 chelation-assisted hydroesterification이다. 최근 전이금속 촉매에 의한 C-H activation을 이용하여 C-C bond 형성과 같은 organic transformation이 활발히 연구되고 있다. 그 중 hydroesterification은 alkene에 activation된 formyl C-H bond를 첨가하여 ester를 형성하는 반응인데 지금까지 보고된 결과를 보면 decarbonylation으로 인한 낮은 수율이 큰 문제가 되고 있어 이를 억제하기 위해 고압의 carbon monoxide를 사용하고 있다. 본 연구에서는 Ru_3(CO)_12와 2-pyridylmethyl formate의 chelation을 통해 formate의 C-H bond를 수월하게 activation 시키고 decarbonylation을 효과적으로 억제할 수 있다고 보았다. Ru과의 chelation에 의해 activation된 formate는 alekene에 첨가되어 one-carbon elongated esters를 높은 수율과 뛰어난 선택성으로 얻을 수 있었다. 이러한 hydoresterification의 chelation-assisted strategy는 hydroamidation에도 적용 시킬 수 있다. 본 연구에서는 2-pyridyl formamide를 directing group으로 사용하여 decarbonylation을 효율적으로 억제시켜 amide를 modest한 수율과 높은 선택성으로 얻을 수 있었다. Part II는 Ru과 Pd 촉매를 이용하여 formate와 organic eletrphile을 tandem reaction으로 coupling 시키는 연구이다. 먼저 formate는 Ru에 의해 decarbonylation되어 alcohol.rhk CO를 제공하고 alcohol은 chelated carbinol ruthenium cluster 상태로 Pd-catalyzed alkoxycarbonylaton cycle에 전이되어 aryl halide와 coupling하여 aryl esters를 형성한다. 이 반응 시스템에서는 formate를 CO의 source로 사용하기 때문에 기존 반응과 달리 toxic한 CO를 직접 사용하지 않아도 된다는 장점이 있다. 이러한 one-pot multiple catalytic system은 단일 촉매보다 다양한 organic trasformation을 가능하게 해준다. Part III는 Ru과 Pd 촉매를 사용하여 aryl halide와 aldehyde를 bimetallic catalysis로 coupling하는 반응이다. Ru 촉매는 aldehyde와 chelation을 통해 formyl C-H bond를 activation시켜 acylruthenium hydride를 형성하고 이 중간체는 aryl halide가 Pd촉매에 의해 활성화된 형태인 halo(aryl)Pd(II) 중간체에 전이되어 catalytic transmetalation에 의해 aryl ketone을 형성한다. 이러한 cooperative catalytic system은 부산물이 당량만큼 생성되는 기존 cross coupling의 단점을 개선시키는 새로운 시스템의 반응이라 할 수 있다. ; Part I is chelation-assisted hydroesterificaition and hydroamidation of alkenes via ruthenium catalysis. The reaction is especially notable due to the fact that it can be carried out with high efficiency even in the absence of carbon monoxide atmosphere. With the introduction of the 2-pyridyl moiety as a chelation group in formate, Ru3(CO)12-catalyzed activation of the formyl C-H bond of formate and subsequent addition of the intermediate to alkenes proceeded with almost complete suppression of decarbonylation. Stereoselectivity of the produced one-carbon elongated esters was good to excellent for the formation of the linear adduct depending on the bulkiness of the alkenes used. This procedure could be readily applied to a variety of olefins such as terminal, internal, cyclic, bicyclic, vinyl ether, and conjugated enone systems with high efficiency and selectivity. It was also amenable to a solvent-free condition. On the basis of the chelation-driven C-H bond activation of formate, a putative mechanism of the Ru-catalyzed hydroesterification of 2-pyridylmethyl formate has been proposed. This research has also developed a practical useful catalytic hydroamidation reaction of alkenes guided by a chelation-assisted strategy. Using 2-pyridyl formamide, decarbonylation could be moderate suppressed with a Ru catalyst during the reaction course, allowing one-carbon elongated amides starting from alkenes in temperate yield and high selectivity without requirement of high pressure CO. Part II is chelation-assisted sequential decarbonylation of formate and alkoxycarbonylation of aryl halides by the Ru and Pd catalyst. An efficient cooperative catalytic system for coupling reaction between a chelating formate and a diverse range of organic electrophiles has been developed to afford aryl and alkenyl esters on the basis of chelation strategy utilizing one-pot employment of Ru and Pd catalyst, in which ruthenium first catalyzes decarbonylation of formate to give CO and a chelated carbinol ruthenium cluster that is subsequently transferred into palladium-catalyzed alkoxycarbonylation cycle. This muti catalytic system has advantages of useful organic transformation. Part III is a cooperative doubly catalytic coupling reaction of aryl halides with aldehyde by a combination of Pd and Ru catalyst. This bimetallic catalysis system for coupling reaction between a chelating aldehyde and organic electrophiles has been developed to afford aryl ketones through Ru catalyzed transmetalation, which is that acylruthenium hydride species are transferred to the halo(aryl)Pd(II) intermediate, in Pd catalyzed coupling reaction. Organic transformations that are difficult to achieve with the action of single catalyst are possible through cooperative multi-catalytic system.