Asymmetric epoxidation, Michael addition, and triple cascade reaction using polymer-supported prolinol-based auxiliaries

Varela, Michael C.; Dixon, Seth; Lam, Kit S.; Schore, Neil E.

doi:10.1016/j.tet.2008.08.013

Cited by 62 publications

(38 citation statements)

References 25 publications

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“…In fact, the next report on polymer-supported diarylprolinol silyl ethers (also in 2008) was a bottom-up approach as well, this time by a research group in California using the more classical free-radical copolymerization of functional monomers together with comonomers (Scheme 14). [54,61] Carbamate-protected proline methyl ester was prepared by carbodiimide-coupling of Boc-proline and methanol. Treatment of this ester with an excess of freshly prepared 4-vinylphenylmagnesium bromide gave protected diarylprolinol 75.…”

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

“…Deprotection and silylation then gave polymer-supported diarylprolinol silyl ether 77 (Scheme 14). [54,61] Interestingly, the researchers also reported the preparation of the same polymer beads by first deprotecting 75 to free amine 78 and then undertaking the suspension polymerization to give 77. However, the yield for the polymerization of 78 was poor, only 29 %.…”

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

“…[54,61] Weinreb amide 79, obtained from coupling of Boc-proline and N,O-dimethylhydroxylamine hydrochloride, was treated with 4-isopropylphenylmagnesium bromide to give ketone 80, which upon addition of 4-vinylphenylmagnesium bromide yielded styrene 81. Suspenwww.eurjoc.orgScheme 14.…”

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

“…Preparation of polymer-supported diarylprolinol by copolymerization of styrenic diarylprolinol crosslinker and styrene. [54,61] Scheme 15. Preparation of polymer-supported diarylprolinol by copolymerization of styrenic diarylprolinol with styrene and DVB.…”

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

“…Preparation of polymer-supported diarylprolinol by copolymerization of styrenic diarylprolinol with styrene and DVB. [54,61] sion copolymerization together with styrene and DVB (crosslinker essential since 81, as opposed to 75, is monostyrenic), followed by deprotection and silylation furnished polymer beads 83. It is imperative to note that the these immobilized diarylprolinols were originally developed for polymer-supported Corey-Bakshi-Shibata (CBS) asymmetric reduction catalysts nearly a decade ago, [61] and only the final silylation of the CBS catalysts into diarylprolinol silyl ethers 77 and 83 were new developments in their 2008 report.…”

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

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Polymer‐Supported Chiral Organocatalysts: Synthetic Strategies for the Road Towards Affordable Polymeric Immobilization

2010

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In this microreview, we highlight the field of polymer‐supported organocatalysis, especially immobilized enamine and iminium organocatalysts. We try to formalize the overall synthetic strategies for polymeric immobilization as spanning the area of two overlapping regions, from a copolymer strategy favoured by low‐valued and small catalysts to a classical post‐modification strategy favoured by valuable and/or large catalysts. Organocatalysis is particularly interesting as it is probably best described as being located in the transitional region, and we will trace the historic and factual origins for the unfortunate predispositions towards post‐modification schemes. In addition, we try to identify affordable and useful syntheses of key organocatalyst immobilization intermediates, as well as polymer supports that are more compatible with a broader range of reaction solvent polarity, something of crucial importance in organocatalysis.

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Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

Section: Polymer-supported Diarylprolinol Silyl Ethersmentioning

confidence: 99%

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Polymer‐Supported Chiral Organocatalysts: Synthetic Strategies for the Road Towards Affordable Polymeric Immobilization

2010

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The Catalytic, Enantioselective Michael Reaction

et al. 2016

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The catalytic enantioselective Michael reaction is the conjugate addition of a resonance‐stabilized carbanion to an electron‐poor olefin (an αβ‐unsaturated carbonyl compound or a related derivative) mediated by substoichiometric amounts of a chiral catalyst that enables stereocontrol in the newly generated stereocenter(s). This reaction allows the direct enantioselective construction of substituted 1,5‐dicarbonyl compounds or related architectures through the appropriate selection of the enolizable carbonyl compound employed as pronucleophile and the Michael acceptor. A variety of catalyst architectures have been described that make it possible to carry out this reaction with superior levels of chemical efficiency and high enantio‐ and stereocontrol, and also under conditions that tolerate a wide variety of functional groups. Both transition metal catalysis and organocatalysis have been employed as methodological approaches for carrying out this reaction in an enantioselective manner. This chapter describes different catalytic systems and methods developed for achieving enantioselective Michael reactions through the end of 2012, including a detailed mechanistic explanation of the different generic modes of substrate activation operating with each type of catalyst and their associated stereochemical aspects. The intention is to provide researchers interested in applying this methodology to their own synthetic strategies with a suitable starting point for identifying an efficient synthetic approach. In addition, the preparation of selected catalysts that are excellent for a particular pairing of substrates in this reaction, together with practical experimental protocols are described and some examples in which these methodologies have been applied to total synthesis have been included. This chapter is limited exclusively to those examples in which the final Michael addition product is obtained after protonation of the conjugate addition intermediate and therefore, tandem, domino, or cascade processes initiated by Michael reactions lie outside the scope of this work. Supplemental references are provided for articles published after the 2012 cut‐off date through the first half of 2015.

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