Angewandte
Communications
Chemie
Olefin Functionalization
Iron-Catalyzed Decarboxylative Alkyl Etherification of Vinylarenes
with Aliphatic Acids as the Alkyl Source
Wujun Jian+, Liang Ge+, Yihang Jiao, Bo Qian, and Hongli Bao*
Abstract: Because of the lack of effective alkylating reagents,
alkyl etherification of olefins with general alkyl groups has not
been previously reported. In this work, a variety of alkyl diacyl
peroxides and peresters generated from aliphatic acids have
been found to enable the first iron-catalyzed alkyl ether-
ification of olefins with general alkyl groups. Primary,
secondary and tertiary aliphatic acids are suitable for this
reaction, delivering products with yields up to 97%. Primary
and secondary alcohols react well, affording products in up to
91% yield.
Carboxylic acids are abundant, inexpensive, and non-toxic
substances extensively used in organic synthesis.[6,7] Carbox-
ylic acid activation through the formation of redox-active
esters is emerging as a powerful strategy for decarboxylative
coupling reactions.[8–10] Peresters and diacyl peroxides are
readily prepared from carboxylic acids and represent another
type of activated carboxylic acids.[11,12] Here, we report the
first decarboxylative alkyl etherification of olefins with
aliphatic acids as the alkyl group source in the presence of
iron catalysts through a carboxylic acid activation strategy
(Scheme 1b).
T
he difunctionalization of olefins is a powerful approach to
install two functional groups on hydrocarbons.[1] Carbon–
carbon and carbon–oxygen bonds are ubiquitous bonds in
nature. The selective difunctionalization of olefins with
carbon-based and oxygen-based groups provides an efficient
strategy to construct molecules with more structural complex-
ity from simple precursors. The efficient oxy-arylation of
olefins has been developed by Toste, Lloyd-Jones, Studer,
Greaney, and Heinrich et al.[2] In contrast, the oxy-alkylation
of olefins has not been well developed. Ishii et al. reported the
first catalytic oxy-alkylation of alkenes with cyclic alkanes and
molecular oxygen via a radical process by using N-hydroxy-
phthalimide.[3a] This pioneering work suffers from poor
chemoselectivity. To further develop this area, radical pre-
cursors and Togniꢀs reagent have been utilized as alkyl
sources.[3] The only example of oxy-alkylation of olefins with
general alkyl groups was reported by Wang et al.[4] This
Re2(CO)9-catalyzed alkyl esterification of vinylarenes applied
hypervalent iodine(III) reagents as the alkylating reagents.
Most of the aforementioned oxy-alkylations of olefins
presumably proceed through a radical pathway. Studies of
radical stabilization energies showed that general alkyl
radicals are poorly stabilized.[5] How to access this type of
radicals at mild condition and keep these radicals under
control in the reaction would be the two key points in the oxy-
alkylation of olefins.
Scheme 1. Oxy-alkylation of alkenes.
We initiated our studies by screening the solvents used in
the alkyl etherification reaction of styrene with lauroyl
peroxide (LPO) in presence of Fe(OTf)2 (Table 1, entries 1–
8). Dioxane was found to be the most efficient solvent for this
reaction and afforded the product in 69% yield. Fe(OTf)3 was
slightly better than Fe(OTf)2 as catalyst and delivered the
product with 70% yield (entry 9). Optimization of the
reaction temperature revealed 508C to be optimal
(entries 10–13). The amount of CH3OH used was examined
and it was found that 6 equiv of CH3OH was the most
effective amount (entries 14–17), generating the product in
yields as high as 82%. Only trace amounts of 3aa were
produced with 20 mol% triflic acid or in the absence of iron
catalyst (entries 18 and 19).
[*] W. Jian,[+] L. Ge,[+] Y. Jiao, B. Qian, Prof. Dr. H. Bao
State Key Laboratory of Structural Chemistry, Key Laboratory of Coal
to Ethylene Glycol and Its Related Technology, Fujian Institute of
Research on the Structure of Matter, University of Chinese Academy
of Sciences
155 Yangqiao Road West, Fuzhou, Fujian 350002 (P.R. China)
E-mail: hlbao@fjirsm.ac.cn
[+] These authors contributed equally to this work.
To further simplify the procedure, we developed a filtra-
tion procedure using peroxides generated in situ. Alkyl diacyl
peroxides and peresters, generated by DCC-mediated dehy-
drative condensation with hydrogen peroxide or tert-butyl
peroxides, were used directly after filtration in the alkyl
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
Angew. Chem. Int. Ed. 2017, 56, 1 – 6
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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