Beilstein J. Org. Chem.2022,18, 217–224, doi:10.3762/bjoc.18.25
on the screening of various bifunctional H-bondingcatalysts, and in this regard, the reaction catalyzed by quinine-derived thiourea catalyst 3b furnished the product 4a in 55% yield and 71% ee (Table 1, entry 5). The other enantiomer was obtained when the reaction was carried out using the
Beilstein J. Org. Chem.2019,15, 2948–2957, doi:10.3762/bjoc.15.290
hydrogen-donating organocatalysts and kinetic experiments suggest that the catalysts bind stronger to the starting silyl ketene acetals than to transition structures thus leading to inefficient rearrangement reactions.
Keywords: DFT calculations; green solvents; H-bondingcatalysts; Ireland–Claisen
. For this, we have compared the uncatalyzed Ireland–Claisen rearrangement with three hydrogen-bond-catalyzed reactions. As model H-bondingcatalysts, we selected diphenylthiourea, Schreiner thiourea, and the corresponding squaramide with bis(trifluoromethyl)phenyl groups. We have evaluated both the (E
, which agrees well with the DFT calculated values. These kinetic measurements support the notion that H-bondingcatalysts bind stronger to starting silyl ketene acetals and thus prevent it from undergoing Ireland–Claisen rearrangement. For more details, see Supporting Information File 1.
Conclusion
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Graphical Abstract
Scheme 1:
Ireland–Claisen rearrangement of allyl esters 1a–c.