Angewandte
Communications
Chemie
Cross-Couplings
Decarbonylative Silylation of Esters by Combined Nickel and Copper
Catalysis for the Synthesis of Arylsilanes and Heteroarylsilanes
Lin Guo, Adisak Chatupheeraphat, and Magnus Rueping*
Abstract: An efficient nickel/copper-catalyzed decarbonyla-
tive silylation reaction of carboxylic acid esters with silylbor-
anes is described. This reaction provides access to structurally
diverse silanes with high efficiency and excellent functional-
group tolerance starting from readily available esters.
we wondered whether it would be possible to develop a more
À
convenient approach for building C Si bonds by a decarbon-
ylative strategy starting from carboxylic acid esters,[10] which,
owing to their ubiquitous nature, are more attractive electro-
philic coupling partners than the more sensitive and less
stable acyl chlorides.
O
rganosilicon compounds constitute an important class of
With these considerations in mind, we began to search for
potential catalysts and nucleophiles for the decarbonylative
silylation of esters. Owing to their air stability, facile synthesis,
and environmentally benign nature, silylborane compounds,
which serve as efficient silicon nucleophiles in copper-
catalyzed transmetalation,[11] have shown high efficiency and
remarkable potential in various organic transformations.[12]
Herein, we present the discovery of a new method for the
nickel-[13] and copper-catalyzed decarbonylative silylation of
esters by using silylborane compounds as coupling partners,
which also features a wide substrate scope (Scheme 1).
intermediates in the synthesis of natural products, drug
molecules, and functional materials.[1] They have attracted
increasing attention in view of their high reactivity as useful
synthetic building blocks as well as their unique physical and
chemical properties.[2] The synthesis of organosilicon com-
pounds is traditionally based on the addition of Grignard or
organolithium reagents to chlorosilanes or cyclosiloxanes.[3]
Alternatively, organosilanes can be prepared by transition-
metal-catalyzed cross-couplings of organohalides with hydro-
silanes[4] or disilanes.[5] Recently, catalytic silylation by C H
À
bond activation has been achieved. However, the regioselec-
tivity was not always satisfactory or additional directing
groups were needed.[6] Therefore, emphasis is directed on
research aimed at finding new synthetic routes for the
synthesis of organosilicon compounds.
Transition-metal-catalyzed decarboxylative/decarbonyla-
tive cross-coupling reactions have recently attracted consid-
erable attention owing to the availability and natural abun-
dance of carboxylic acids and their derivatives as alternatives
to halides and organometallic reagents.[7] Unlike the direct
decarboxylation of carboxylic acids, decarbonylative cou-
plings can normally be accessed by extrusion of carbon
monoxide from acyl–metal species, which can be generated by
oxidative addition of carboxylic acid derivatives to metal
complexes. Whereas many methods for carbon–carbon bond-
forming reactions have been developed by employing differ-
ent carbonyl precursors, very little is known about carbon–
heteroatom, and in particular carbon–silicon, bond-forming
reactions by decarbonylative processes. Krafft and co-work-
ers reported a palladium-catalyzed decarbonylative coupling
of acyl chlorides with disilanes,[8] and Tsuji and co-workers
developed a palladium-catalyzed 1,4-carbosilylation.[9] Hence
Scheme 1. Nickel/copper-catalyzed decarbonylative silylation of esters.
We started our investigations by examining the reactivity
of phenyl 2-naphthoate (1a) with silylborane 2a in the
presence of nickel and copper catalysts (Table 1).[14] First, we
evaluated various ligands and obtained a promising result
when employing tri-n-butylphosphine as the ligand and
cesium fluoride as the base (entries 1–4). As the nature of
the base plays a critical role for the success of the decarbon-
ylative cross-coupling, various bases were evaluated. Replac-
ing cesium fluoride with potassium fluoride under otherwise
identical reaction conditions slightly improved the yield
(entry 9) whereas the use of other bases or no base gave
rather unsatisfying results (entries 5–8). Although different
co-catalysts could be utilized (entries 10–12), the best result
was obtained with copper(II) fluoride, which confirmed that
the copper-based co-catalyst plays a crucial role in activating
the Si B bond.[15] Moreover, a slight increase in temperature
[*] M. Sc. L. Guo, M. Sc. A. Chatupheeraphat, Prof. Dr. M. Rueping
Institute of Organic Chemistry, RWTH Aachen University
Landoltweg 1, 52074 Aachen (Germany)
À
gave a dramatic change in reactivity, providing 3a in 83%
yield (entry 13). Further evaluation resulted in the optimized
reaction conditions, which entailed the use of 2.0 equiv of the
silylborane nucleophile (entry 14). A control experiment
further revealed that the reaction did not occur in the
absence of the nickel catalyst (entry 15).
E-mail: Magnus.Rueping@rwth-aachen.de
Prof. Dr. M. Rueping
King Abdullah University of Science and Technology (KAUST)
KAUST Catalysis Center (KCC)
Thuwal, 23955-6900 (Saudi Arabia)
Encouraged by our initial results, we decided to examine
a series of aryl esters as electrophiles to determine the scope
Supporting information for this article can be found under:
Angew. Chem. Int. Ed. 2016, 55, 1 – 5
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!
Guo, Lin
