Co-catalyst enhancement of enantioselective PTC Michael additions involving glycine imines

Lygo, Barry; Beynon, Christopher; Lumley, Christopher; McLeod, Michael C.; Wade, Charles E.

doi:10.1016/j.tetlet.2009.02.123

Cited by 39 publications

(27 citation statements)

References 37 publications

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“…The sequence features an asymmetric conjugate addition of 7 to vinyl ketones in the presence of catalyst 2 h, followed by acid-catalyzed imine exchange and catalytic hydrogenation (Scheme 61). [82] The same strategy was used by Shibata and co-workers for the asymmetric synthesis of b-trifluoromethylpyrroline carboxylates, such as 109. The use of the bulky adamantyl glycinate 108 with catalyst 1 h led to the product with high stereoselectivity (Scheme 62).…”

Section: Methodsmentioning

confidence: 99%

Recent Developments in Asymmetric Phase‐Transfer Reactions

2013

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Phase-transfer catalysis has been recognized as a powerful method for establishing practical protocols for organic synthesis, because it offers several advantages, such as operational simplicity, mild reaction conditions, suitability for large-scale synthesis, and the environmentally benign nature of the reaction system. Since the pioneering studies on highly enantioselective alkylations promoted by chiral phase-transfer catalysts, this research field has served as an attractive area for the pursuit of "green" sustainable chemistry. A wide variety of asymmetric transformations catalyzed by chiral onium salts and crown ethers have been developed for the synthesis of valuable organic compounds in the past several decades, especially in recent years.

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Section: Methodsmentioning

confidence: 99%

Recent Developments in Asymmetric Phase‐Transfer Reactions

2013

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“…As previously discussed, the aryloxides are known to act as Lewis bases able to activate silylated pro‐nucleophiles . Nevertheless, their use as Brønsted bases as also been reported but remained limited in the literature certainly due to their p K a values (ranging from 13 to 19) . Our contribution to develop chiral ammonium aryloxides as Brønsted base catalysts led to significant advances set out below.…”

Section: Protonation or Deprotonation: That Is The Question?mentioning

confidence: 93%

New Developments in Chiral Cooperative Ion Pairing Organocatalysis by Means of Ammonium Oxyanions and Fluorides: From Protonation to Deprotonation Reactions.

2016

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This personal account summarizes our contribution to the ion pairing organocatalysis mainly by use of chiral quaternary or tertiary ammonium fluorides, aryloxides and carboxylates. Starting from an experimental observation, we were able to develop several approaches for the enantioselective protonation of silyl enolates and enol esters giving rise to chiral carbonyl compounds bearing a stereogenic center at the α-position. Moving from protonation to deprotonation reactions, chiral ammonium ion pair catalysts were successfully applied to several asymmetric transformations such as an Henry reaction or a direct vinylogous aldol reaction to cite a few. An outlook of further possible developments in this field of research will also be discussed.

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“…The first example, published by the Lygo group in 2009, deals with the Michael addition of tert-butylglycine imines 24 to various Michael acceptors in the presence of DHCD + + 1,ArO À ,f urnishing the correspondingadducts 25 in moderatetoexcellent yields (63-96 %) and high enantioselectivities( 89-98 %) (Scheme 12). [27] Although no reaction took place in the presence of DHCD + + 1,Br À and solid KOH, high conversions and excellent enantioselectivities could be achieved by simply adding 10 mol %o fm esitol. This finding argues in favor of DHCD + + 1,ArO À as the reactive catalytic species.…”

Section: Application As Brønsted Base Organocatalystsmentioning

confidence: 99%