The highly enantioselective alkynylation of isatins, catalyzed by a bifunctional guanidine/CuI catalyst under mild reaction conditions, is described. The reaction is broad in scope with respect to alkyl/aryl-substituted terminal alkynes and substituted isatins, thus affording bioactive propargylic alcohols in excellent yields and enantioselectivities.
The asymmetric C-H insertion of α-diazoesters into 1-alkynes was achieved using chiral cationic guanidinium salts and copper(I) complexes. Optically active 2,4-disubstituted allenoates were generated under mild reaction conditions from various α-diazoesters and 1-alkynes in high yield (up to 99%) and enantioselectivity (up to 97:3 e.r.). Control experiments excluded the possibility of an asymmetric isomerization of alkynoates.
Isatin-derived ketimines undergo enantioselective alkynylation reactions in the presence of copper iodide and easily accessible guanidine-amides. The corresponding 3-alkynyl-3-aminooxyindoles are obtained in up to 95% yield and 96% ee. The guanidine plays a role in the formation of copper acetylide and the enantiodetermining step and the basic additive is excluded.
A chiral ytterbium(III)-N,N'-dioxide catalyst system has been developed for the catalytic direct asymmetric vinylogous Michael addition of 3-alkylidene oxindoles to chalcones, delivering the γ-substituted alkylideneoxindoles in high yields, enantioselectivities and good Z/E selectivities under mild reaction conditions.
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