10.1002/anie.201705431
Angewandte Chemie International Edition
COMMUNICATION
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cyclopropene unit in 2a to the metal center in B could afford two
possible transition states C-1 and C-2, in which C-1 is favored
as it has less steric repulsion between the substituents of the
cyclopropene skeleton in 2a and the catalyst ligand. The
insertion of the cyclopropene unit into the pyridylmethyl−Y bond
in C-1 would give D, which after deprotonation of another
molecule of 1a by the cyclopropyl−Y bond affords the final
product 3a and regenerates the active species B. The kinetic
isotope effect (KIE) studies suggest that C(sp3)−H bond
cleavage is involved in the rate-determining step (see supporting
information).
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In summary, we have achieved for the first time the
enantioselective C(sp3)−H bond addition of 2-methyl azaarenes
to various cyclopropenes and norbornenes by using a chiral half-
sandwich rare-earth metal catalyst such as TIPS-Y. This
protocol has afforded
a
series of chiral pyridylmethyl-
functionalized cyclopropane and norbornane derivatives in high
yields and excellent enantioselectivity in a 100% atom-efficient
manner. Functional groups such as SiMe3, linear alkenyl, and
aryl halides are compatible. This unique catalytic transformation
could be ascribed to the strong heteroatom affinity of the rare-
earth metal ions and the high activity of the cationic rare-earth
metal alkyl species towards both C–H activation and C=C
double bond insertion, as well as to the well-defined chiral Cp
ligand environment. Studies on the synthesis and application of
chiral half-sandwich rare-earth alkyl catalysts for asymmetric C–
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fashion is usually much more difficult than that of a sp2 C−H bond. For
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H
transformations and related reactions can be fruitfully
prospected.
Acknowledgements
This work was supported by a Grant-in-Aid for Scientific
Research (S) (No. 26220802) from JSPS. Y.L. thanks RIKEN for
a Foreign Postdoctoral Researcher (FPR) fellowship.
Keywords: cyclopropenes • sp3 C-H bond addition • chiral
yttrium catalyst • pyridine• norbornene
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