An exploration of asymmetric Baylis–Hillman reactions catalyzed by quinidine-derived chiral amines

Shi, Min; Jiang, Jian-Kang

doi:10.1016/s0957-4166(02)00485-8

Cited by 84 publications

(38 citation statements)

References 11 publications

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“…We began our bifunctional studies 15 by adding 10 mol % of the metal complexes that worked best for our imine alkylations (and that were conveniently on our laboratory shelves), including Rh(PPh 3 ) 3 OTf and Cu(PPh 3 ) 2 ClO 4 , to the standard reaction conditions to form β-lactams. To our surprise, the overall yield decreased in the presence of the respective metal.…”

Section: Bifunctional Systemmentioning

confidence: 99%

“…A plausible explanation is that the ligand exchange between the quinuclidine nitrogen and the imino ester must favor the bidentate binding afforded by the imino ester. Having firmly established In(OTf) 3 as the best overall Lewis acid cocatalyst for our reaction, we applied this system to various substrates to determine the scope of its influence ( Figure 1). Generally, the yields increase by 1.5-2-fold with the In III cocatalyst, and enantioselectivity is excellent and virtually unaffected by the metal.…”

Section: Bifunctional Systemmentioning

confidence: 99%

“…Drawing an analogy to our bifunctional β-lactam system, 15b we believed that activation of the potentially chelating benzoquinone diimide by a Lewis acid cocatalyst may increase the rate of the desired reaction. We tested our hypothesis by screening the metal salts that were most successful in our bifunctional β-lactam method, namely, Al(OTf) 3 , In(OTf) 3 , Sc(OTf) 3 , and Zn(OTf) 2 . Our results demonstrated an increase in yield for all four cocatalysts, although Zn(OTf) 2 proved to be the best and most cost-effective of the group.…”

Section: O-benzoquinone Diimidesmentioning

confidence: 99%

“…As in the earlier cases, we wanted to make our method more useful by optimizing the yields through the use of a Lewis acid cocatalyst. A number of metal triflates were screened for this purpose, and we found that In(OTf) 3 , Zn(OTf) 2 , and Sc(OTf) 3 provided increased yields. We believe the Lewis acid coordinates to the quinone imide to enhance its electrophilicity, thereby increasing the reaction rate and ultimately the yield.…”

Section: O-benzoquinone Imidesmentioning

confidence: 99%

“…Of note, Shi has reported a lithium-assisted BaylisHillman reaction catalyzed by cinchona alkaloid derivatives. 3 An asymmetric cyanosilylation of ketones was proposed by Shibasaki et al to occur via a tethered Lewis acid/phosphine oxide system based on glucose. 4 These authors have also developed a series of tethered catalysts based on a BINOL template, which have been applied to a variety of reactions.…”

Section: Introductionmentioning

confidence: 99%

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Bifunctional Asymmetric Catalysis: Cooperative Lewis Acid/Base Systems

et al. 2008

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In the field of catalytic, asymmetric synthesis, there is a growing emphasis on multifunctional systems, in which multiple parts of a catalyst or multiple catalysts work together to promote a specific reaction. These efforts, in part, are result-driven, and they are also part of a movement toward emulating the efficiency and selectivity of nature's catalysts, enzymes. In this Account, we illustrate the importance of bifunctional catalytic methods, focusing on the cooperative action of Lewis acidic and Lewis basic catalysts by the simultaneous activation of both electrophilic and nucleophilic reaction partners. For our part, we have contributed three separate bifunctional methods that combine achiral Lewis acids with chiral cinchona alkaloid nucleophiles, for example, benzoylquinine (BQ), to catalyze highly enantioselective cycloaddition reactions between ketene enolates and various electrophiles. Each method requires a distinct Lewis acid to coordinate and activate the electrophile, which in turn increases the reaction rates and yields, without any detectable influence on the outstanding enantioselectivities inherent to these reactions. To place our results in perspective, many important contributions to this emerging field are highlighted and our own reports are chronicled. PAULL et al.

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Section: Bifunctional Systemmentioning

confidence: 99%

Section: Bifunctional Systemmentioning

confidence: 99%