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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.


Tan’s enantioselective addition of secondary phosphine oxides and thiols to N-arylitaconimides.
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C23: Tan’s enantioselective addition of secondary phosphine oxides and thiols to N-arylitaconimides.

Mentions: Tan and co-workers have investigated the conjugate addition–enantioselective protonation of N-arylitaconimides 95 using a C2-symmetric guanidine catalyst (Scheme 23) [24,46]. Because E- and Z-enolates can exhibit different enatiofacial selectivity, the use of a cyclic imide ensured exclusive formation of the Z-enolate. During optimization, it was found that an N-aryl group containing 2,6-disubstitution was crucial for obtaining high levels of enantioselectivity. Addition of a variety of bis-aryl secondary phosphine oxides furnished 96 in high yield and enantioselectivity (Scheme 23) [24]. Thiols also added efficiently to itaconimide 95 using the same guanidine catalyst system. In general, sterically hindered tertiary thiols added with higher enantioselectivity (85.5:14.5 to 88:22 er) than aromatic thiols (72:28 to 79.5:20.5 er) (Scheme 23) [46]. This enantioselective addition process could be applied to a racemic mixture of axially chiral N-(2-tert-butylphenyl)itaconimide (98), furnishing atropisomers 99a and 99b as a stable and separable 1:1 mixture. A higher enantioselectivity was observed for the anti-diastereomer (Scheme 23).


Conjugate addition – enantioselective protonation reactions
Tan’s enantioselective addition of secondary phosphine oxides and thiols to N-arylitaconimides.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

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

C23: Tan’s enantioselective addition of secondary phosphine oxides and thiols to N-arylitaconimides.
Mentions: Tan and co-workers have investigated the conjugate addition–enantioselective protonation of N-arylitaconimides 95 using a C2-symmetric guanidine catalyst (Scheme 23) [24,46]. Because E- and Z-enolates can exhibit different enatiofacial selectivity, the use of a cyclic imide ensured exclusive formation of the Z-enolate. During optimization, it was found that an N-aryl group containing 2,6-disubstitution was crucial for obtaining high levels of enantioselectivity. Addition of a variety of bis-aryl secondary phosphine oxides furnished 96 in high yield and enantioselectivity (Scheme 23) [24]. Thiols also added efficiently to itaconimide 95 using the same guanidine catalyst system. In general, sterically hindered tertiary thiols added with higher enantioselectivity (85.5:14.5 to 88:22 er) than aromatic thiols (72:28 to 79.5:20.5 er) (Scheme 23) [46]. This enantioselective addition process could be applied to a racemic mixture of axially chiral N-(2-tert-butylphenyl)itaconimide (98), furnishing atropisomers 99a and 99b as a stable and separable 1:1 mixture. A higher enantioselectivity was observed for the anti-diastereomer (Scheme 23).

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.