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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.


Sodeoka’s enantioselective addition of amines to N-benzyloxycarbonyl acrylamides 75 and 77.
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C18: Sodeoka’s enantioselective addition of amines to N-benzyloxycarbonyl acrylamides 75 and 77.

Mentions: Many examples of conjugate addition–enantioselective protonation have been reported using carbon and sulfur nucleophiles, conversely relatively few examples have been reported using amines as nucleophiles. Sodeoka and co-workers have described the synthesis of β-aminocarbonyl compounds via the enantioselective addition of amine salts 74 to N-benzyloxycarbonyl acrylamides 75 and 77 catalyzed by a palladium-μ-hydroxo complex 79 (Scheme 18) [38–40]. Hii has used the same catalyst system and reported comparable yields and slightly lower enantioselectivities for the addition of para-substituted anilines to α,β-unsaturated imines [41]. Gil and Collin have also reported on the same reaction as Sodeoka, but using a samarium-BINOL catalyst system, which proceeded with lower enantioselectivity [42]. Sodeoka found that minimizing the concentration of free amine present in the reaction mixture by using the triflate salts of the amines was crucial for obtaining high enantioselectivity. Excess free amine resulted in catalyst deactivation and a racemic background reaction. Electron-rich and neutral aromatic amines added to both acyclic and cyclic N-benzyloxycarbonyl acrylamides 75 and 77 in moderate to good yields and high enantioselectivity (Scheme 18,b). Due to their attenuated nucleophilicity, electron-deficient amines were unreactive under the standard reaction conditions. Addition of 0.5 equivalents of free amine was found to be optimal, providing the product with excellent enantioselectivity (Scheme 18). Notably, the authors did not observe any side reaction between the palladium and aryl bromide or aryl iodide groups.


Conjugate addition – enantioselective protonation reactions
Sodeoka’s enantioselective addition of amines to N-benzyloxycarbonyl acrylamides 75 and 77.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

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

C18: Sodeoka’s enantioselective addition of amines to N-benzyloxycarbonyl acrylamides 75 and 77.
Mentions: Many examples of conjugate addition–enantioselective protonation have been reported using carbon and sulfur nucleophiles, conversely relatively few examples have been reported using amines as nucleophiles. Sodeoka and co-workers have described the synthesis of β-aminocarbonyl compounds via the enantioselective addition of amine salts 74 to N-benzyloxycarbonyl acrylamides 75 and 77 catalyzed by a palladium-μ-hydroxo complex 79 (Scheme 18) [38–40]. Hii has used the same catalyst system and reported comparable yields and slightly lower enantioselectivities for the addition of para-substituted anilines to α,β-unsaturated imines [41]. Gil and Collin have also reported on the same reaction as Sodeoka, but using a samarium-BINOL catalyst system, which proceeded with lower enantioselectivity [42]. Sodeoka found that minimizing the concentration of free amine present in the reaction mixture by using the triflate salts of the amines was crucial for obtaining high enantioselectivity. Excess free amine resulted in catalyst deactivation and a racemic background reaction. Electron-rich and neutral aromatic amines added to both acyclic and cyclic N-benzyloxycarbonyl acrylamides 75 and 77 in moderate to good yields and high enantioselectivity (Scheme 18,b). Due to their attenuated nucleophilicity, electron-deficient amines were unreactive under the standard reaction conditions. Addition of 0.5 equivalents of free amine was found to be optimal, providing the product with excellent enantioselectivity (Scheme 18). Notably, the authors did not observe any side reaction between the palladium and aryl bromide or aryl iodide groups.

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.