C O M M U N I C A T I O N S
Table 2. In(OH)3-Catalyzed Deoxygenative Chlorination of
Various Carbonyls 1 by HSiMe2Cl (2b)a
give the iodide 8 (eq 3). Although details of the process are not
clear, HSiMe2I generated in situ is expected to cause the iodination.9
To expand this methodology, the simultaneous induction of allyl
and chlorine moieties was attempted (eq 4), where allylsilylation
is required instead of hydrosilylation. The new C-C and C-Cl
bonds could be formed on the carbonyl carbon of the ketone 1b
and the aldehyde 1s with release of oxygen to afford 9b and 9s,
respectively. It is noted that even the ketone successfully gave the
product despite the difficulty in its catalytic allylation using
allylsilane. The indium-catalyzed deoxygenation step might be a
driving force for this process.
In summary, we have achieved novel deoxygenative halogenation
catalyzed by In(OH)3 using functionalized halosilanes. This method
provides an unprecedented synthetic route to organic halides.
Further extensions of this work are now in progress.
a All reactions were carried out with carbonyls 1 (2.0 mmol), chlorosilane
2b (2.4 mmol), and In(OH)3 (0.1 mmol) in chloroform (4 mL). b InCl3
was used instead of In(OH)3. c Chlorosilane 2b (4.4 mmol) was used.
d (4-Methoxyphenyl)ethane (5) was obtained in 38% yield. e The ether
(PhCH2CH2)2O (6) was obtained in 70% yield. f Cis/trans ) 12/88.
Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology, of the Japanese Government.
Supporting Information Available: Reaction procedure and
spectroscopic details of new compounds (PDF). This material is
Scheme 2. Plausible Reaction Path
References
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yield (entry 10), and the latter gave a dialkyl ether (entry 11).
Aliphatic ketone afforded the sec-alkyl chlorides 3m and 3n at
higher temperature (entries 13 and 14). Functionalized ketones 1o-r
selectively afforded the corresponding chlorides 2o-r, respectively
(entries 15-18).
A plausible reaction path is illustrated in Scheme 2. At first,
hydrosilylation takes place to give silyl ether C, which then is
activated by the indium catalyst to give chloride 3 with leaving of
the siloxy group. This reaction path is confirmed by the fact that
the silyl ether 7, separately prepared by the conventional method,
was facilely transformed to the corresponding chloride 3a by In-
(OH)3 catalyst (eq 2).6 The formation of undesired products D and
E (corresponding to the products 5 and 6 in entries 10 and 11 in
Table 2) also supports the initial generation of C.7
(6) According to the advice of a referee, we examined the chlorination of
chlorosilyl ether derived from (R)-1-phenylethanol, where complete
racemization was observed (see the Supporting Information). Although
this result indicates a SN1 mechanism, the detail and generality of this
stereochemistry are under investigation.
(7) We can rule out a reaction course that includes chlorosilylation of carbonyls
because of the low nucleophilicity of chloride.
(8) Yasuda, M.; Onishi, Y.; Ueba, M.; Miyai, T.; Baba, A. J. Org. Chem.
2001, 66, 7741-7744.
(9) We confirmed that the product 8 was not obtained by the halogen-exchange
from the corresponding chloride 3m with LiI. Because the yield of
deoxygenative iodination product 8 was considerably higher than that of
deoxygenative chlorination (see Table 2, entry 12), the iodosilyl species
is probably generated in situ.
Moderate Lewis acidity and oxophilicity are plausibly important
for achievement of this catalytic cycle because strong Lewis acids
seem to be trapped by oxygen during the reaction course, which
would be the case of ineffective Lewis acids noted in Table 1. High
desiloxylation ability of the indium catalyst8 should accelerate the
reaction from silyl ether to chloride 3.
Deoxygenative iodination was succeeded by addition of LiI to
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