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Conjugate addition – enantioselective protonation reactions

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ABSTRACT

The addition of nucleophiles to electron-deficient alkenes represents one of the more general and commonly used strategies for the convergent assembly of more complex structures from simple precursors. In this review the addition of diverse protic and organometallic nucleophiles to electron-deficient alkenes followed by enantioselective protonation is summarized. Reactions are first categorized by the type of electron-deficient alkene and then are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals.

No MeSH data available.


Frost’s enantioselective additions to dimethyl itaconate.
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C11: Frost’s enantioselective additions to dimethyl itaconate.

Mentions: As shown in Scheme 11, Frost and co-workers have also investigated conjugate addition–enantioselective protonation by the addition of potassium organotrifluoroborates 49 into dimethyl itaconate (50) in the presence of a rhodium(I) catalyst and (R)-BINAP ligand (43, Fig. 2) [31]. During optimization they found that switching to potassium organotrifluoroborates from organoboronic acids was necessary to achieve high enantioinduction. Additionally, the enantioselectivity was highly dependent on the solvent system; the enantioselectivity in benzene was significantly higher than in toluene or dioxane. Electron rich, neutral, and poor organotrifluoroborates were good substrates; however, ortho-substitution was not compatible and provided only trace product. In a subsequent publication, Frost reported that using the same catalyst system, phenyltrimethoxysilane (49a) could be added to dimethyl itaconate (50) with modest enantioselectivity and without defining the absolute configuration of the major stereoisomer (Scheme 11) [32].


Conjugate addition – enantioselective protonation reactions
Frost’s enantioselective additions to dimethyl itaconate.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979737&req=5

C11: Frost’s enantioselective additions to dimethyl itaconate.
Mentions: As shown in Scheme 11, Frost and co-workers have also investigated conjugate addition–enantioselective protonation by the addition of potassium organotrifluoroborates 49 into dimethyl itaconate (50) in the presence of a rhodium(I) catalyst and (R)-BINAP ligand (43, Fig. 2) [31]. During optimization they found that switching to potassium organotrifluoroborates from organoboronic acids was necessary to achieve high enantioinduction. Additionally, the enantioselectivity was highly dependent on the solvent system; the enantioselectivity in benzene was significantly higher than in toluene or dioxane. Electron rich, neutral, and poor organotrifluoroborates were good substrates; however, ortho-substitution was not compatible and provided only trace product. In a subsequent publication, Frost reported that using the same catalyst system, phenyltrimethoxysilane (49a) could be added to dimethyl itaconate (50) with modest enantioselectivity and without defining the absolute configuration of the major stereoisomer (Scheme 11) [32].

View Article: PubMed Central - HTML - PubMed

ABSTRACT

The addition of nucleophiles to electron-deficient alkenes represents one of the more general and commonly used strategies for the convergent assembly of more complex structures from simple precursors. In this review the addition of diverse protic and organometallic nucleophiles to electron-deficient alkenes followed by enantioselective protonation is summarized. Reactions are first categorized by the type of electron-deficient alkene and then are further classified according to whether catalysis is achieved with chiral Lewis acids, organocatalysts, or transition metals.

No MeSH data available.