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vide evidence for the influence of the silane on
the selectivity. The reaction of 5 equivalents of
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generated the major product in which the silyl
group is installed meta to the larger OTIPS group
at the less electron-rich position of the arene (82:18
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tion of 5 equivalents of 21a with HSiMe(OTMS)2
gave predominantly the product in which the silyl
group is installed para to the larger group (7:93
minor:major isomers). We ascribe this change in
selectivity to the unfavorable placement of the
bulky SiMe(OTMS)2 group meta to the OTIPS
group on the arene in the latter transformation.
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Acknowledgments: We thank the NSF (CHE-1213409) for
financial support, Johnson-Matthey for a gift of [Ir(cod)OMe]2,
and T. W. Wilson for helpful discussions. A provisional
patent application on this work has been submitted.
Conclusions
The intermolecular, rhodium-catalyzed silylation
of arenes that we report here occurs under mild
conditions, with arene as the limiting reagent and
with regioselectivities that complement or sur-
pass those of other arene functionalizations. Sev-
eral factors lead to the selectivity and synthetic
utility of the silylation reaction. First, the silicon
reagent is sterically demanding. Assuming the in-
termediate that cleaves the aryl C–H bond con-
tains a silyl group on the metal, the size of the
silane reagent, along with the size of the ancillary
ligands, control the degree of regioselectivity.
Second, two of the substituents on the silane are
bound to silicon through oxygen, and a silicon-
heteroatom bond is typically required for many
of the transformations of arylsilanes at the C–Si
bond. The origin of the remote selectivity remains
to be defined. However, our results suggest that
a wide scope of functionalization reactions with
remote regiocontrol should be achievable through
Supplementary Materials
Materials and Methods
Figs. S1 to S3
Table S1
References (45–58)
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Int. Ed. 52, 8984–8989 (2013).
29. HSiMe(OTMS)2 is commercially available.
30. For applications of phosphine-ligated rhodium catalysts
in intramolecular silylation reactions, see (23, 24).
31. Silylcyclohexane [GC–mass spectrometry; mass/charge
ratio = 289.1; M-CH3], from hydrosilylation of the hydrogen
acceptor, cyclohexene, is the only major side product.
4 November 2013; accepted 14 January 2014
10.1126/science.1248042
Dendritic Inhibition in the
Hippocampus Supports Fear Learning
Matthew Lovett-Barron,1,2* Patrick Kaifosh,1,2* Mazen A. Kheirbek,2,3 Nathan Danielson,1,2
Jeffrey D. Zaremba,1,2 Thomas R. Reardon,1,2 Gergely F. Turi,2 René Hen,1,2,3
Boris V. Zemelman,4 Attila Losonczy1,2,5
†
judicious choice of ancillary ligands and reagents Fear memories guide adaptive behavior in contexts associated with aversive events. The hippocampus
with appropriate steric bulk.
forms a neural representation of the context that predicts aversive events. Representations of
context incorporate multisensory features of the environment, but must somehow exclude sensory
features of the aversive event itself. We investigated this selectivity using cell type–specific imaging
and inactivation in hippocampal area CA1 of behaving mice. Aversive stimuli activated CA1 dendrite-
targeting interneurons via cholinergic input, leading to inhibition of pyramidal cell distal dendrites
receiving aversive sensory excitation from the entorhinal cortex. Inactivating dendrite-targeting
interneurons during aversive stimuli increased CA1 pyramidal cell population responses and prevented
fear learning. We propose subcortical activation of dendritic inhibition as a mechanism for exclusion
of aversive stimuli from hippocampal contextual representations during fear learning.
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versive stimuli cause animals to asso- defensive behaviors during future exposure to
ciate their environmental context with the context. This process of contextual fear con-
A
these experiences, allowing for adaptive ditioning (CFC) is dependent upon the brain
857