Limits...
Conjugate addition – enantioselective protonation reactions

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.


Ellman’s enantioselective addition of thioacids to α,β,β-trisubstituted nitroalkenes.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

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

C38: Ellman’s enantioselective addition of thioacids to α,β,β-trisubstituted nitroalkenes.

Mentions: Ellman and co-workers, in the second example of conjugate addition–enantioselective protonation with nitroalkenes, showed that thioacids 160 could be added in high yields and with high enantioselectivity to α,β,β-trisubstituted nitroalkenes 161 using a thiourea organocatalyst 101b (Scheme 38) [66]. This report was the first example of enantioselective addition to a trisubstituted nitroalkene and was the first example of conjugate addition–enantioselective protonation using a fully substituted alkene. Nitroalkenes that were activated by the incorporation of an oxetane or N-Boc-azetidine ring at the β-position reacted well with both thioacetic acid and thiobenzoic acid (Scheme 38). Various R2 substituents were compatible with the reaction, including an isopropyl group and a pendent methyl ester. Generally, the azetidine nitroalkenes provided the 1,2-nitrothioacetates in higher yields and enantioselectivity (81–99% yield, 95:5 to 98:2 er). The oxetane and N-Boc azetidine nitroalkenes were activated toward conjugate addition by the release of ring-strain. However, thioacetic acid (160a) also adds in good yield and high enantioselectivity to unstrained nitroalkenes 163 (Scheme 38). Additions to β-cyclohexyl and β-4-tetrahydropyran nitroalkenes as well as an acyclic β,β-dimethyl nitroalkene all proceeded with good conversion when the reaction temperature was raised to −25 °C.


Conjugate addition – enantioselective protonation reactions
Ellman’s enantioselective addition of thioacids to α,β,β-trisubstituted nitroalkenes.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

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

C38: Ellman’s enantioselective addition of thioacids to α,β,β-trisubstituted nitroalkenes.
Mentions: Ellman and co-workers, in the second example of conjugate addition–enantioselective protonation with nitroalkenes, showed that thioacids 160 could be added in high yields and with high enantioselectivity to α,β,β-trisubstituted nitroalkenes 161 using a thiourea organocatalyst 101b (Scheme 38) [66]. This report was the first example of enantioselective addition to a trisubstituted nitroalkene and was the first example of conjugate addition–enantioselective protonation using a fully substituted alkene. Nitroalkenes that were activated by the incorporation of an oxetane or N-Boc-azetidine ring at the β-position reacted well with both thioacetic acid and thiobenzoic acid (Scheme 38). Various R2 substituents were compatible with the reaction, including an isopropyl group and a pendent methyl ester. Generally, the azetidine nitroalkenes provided the 1,2-nitrothioacetates in higher yields and enantioselectivity (81–99% yield, 95:5 to 98:2 er). The oxetane and N-Boc azetidine nitroalkenes were activated toward conjugate addition by the release of ring-strain. However, thioacetic acid (160a) also adds in good yield and high enantioselectivity to unstrained nitroalkenes 163 (Scheme 38). Additions to β-cyclohexyl and β-4-tetrahydropyran nitroalkenes as well as an acyclic β,β-dimethyl nitroalkene all proceeded with good conversion when the reaction temperature was raised to −25 °C.

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.