Structure and reactivity of bis(iodozincio)methane in tetrahydrothiophene

Article abstract of DOI:10.1055/s-1999-2877

Addition of tetrahydrothiophene (THT) to a THF solution of bis(iodozincio)methane modified the stability and reactivity: EXAFS analysis indicated that THT stabilizes bis(iodozincio)methane in a monomeric structure; the species reacts with acyl chlorides to give 1,3-diketones.

Full text of DOI:10.1055/s-1999-2877

LETTER
1471
Structure and Reactivity of Bis(iodozincio)methane in Tetrahydrothiophene
Seijiro Matsubara,* Yuhei Yamamoto, Kiitiro Utimoto
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan
Fax: 75-753-4863; E-mail: matsubar@mc.kyoto-u.ac.jp
Received 24 June 1999
Abstract: Addition of tetrahydrothiophene (THT) to a THF solu-
tion of bis(iodozincio)methane modified the stability and reactivity:
EXAFS analysis indicated that THT stabilizes bis(iodozincio)meth-
ane in a monomeric structure; the species reacts with acyl chlorides
to give 1,3-diketones.
Scheme 2
Key words: zinc, 1,3-diketone, dimetal, THT, EXAFS
Table 1 Preparation of 1,3-Diketones by the Reaction of Acyl Chlo-
ride with Bis(iodozincio)methane (1) in THF–THT a
The high synthetic potential of gem-dimetallic reagents
has been extensively studied,1 but any study for control-
ling the reactivity by adding ligand or solvent has not been
examined. Recently we reported a preparation of bis(io-
dozincio)methane (1), 1,1-bis(iodozincio)ethane,1f and
bis(bromozincio)methyltrimethyl-silane1h from the corre-
sponding gem-dihalides by Pb-catalyzed reaction with
zinc in THF. These reagents realized the following trans-
formations; olefination of carbonyl compounds,1f three
component coupling by connection of two different elec-
aacyl chloride (2.0 mmol), bis(iodozincio)methane (0.4 M THF solu-
trophiles on the dimetallated carbon.1g,h 1,3-Diketones
tion, 2.0 mmol), and THT (5 ml) were used. bIsolated yields. cWithout
THT, 2 is formed quantitatively without forming 3 in all cases.
were produced by the direct reaction with acyl cyanides.2
A use of acyl chloride instead of acyl cyanides lead to the
reaction of acyl chloride with THF, which afforded 4-io-
In entries 4–6, the reactions afforded the 1,3-diketones 3
with accompanying 2 that is formed from THF and acyl
chloride. This problem was overcome by removing THF
from the reagent. To a THF solution of 1 (0.4 M, 2.0
mmol), THT (7.5 ml) was added and stirred for 5 min. The
mixture was concentrated in vacuo at 0 °C until a half vol-
ume of the mixture was removed. An selective evapora-
tion of THF from the mixture, owing to the difference of
boiling points, gave a THT solution of 1 that was free
from THF.5 One may think that a concentration of 1 in
THF in vacuo before an addition of THT will offer a sim-
ple procedure, but the removal of THF without adding
THT afforded the solid which would not been dissolved
into THF and THT. A direct concentration from 1 in THF
caused a structural change which may produce the poly-
meric compound as being discussed later in the text. A
treatment of 2-naphthoyl chloride with thus obtained THT
solution of 1 gave 1,3-diketone 3d in 86% yield and did
not afford 2d. The 1H NMR spectra of 1 in THF–THT im-
plies an effective coordination of THT to the dizinc com-
pound. A methylene proton signal of 1 in THF appears at
–1.12 ppm (20 °C) were shifted to –0.90 ppm by an addi-
tion of THT. A THT solution of 1 also gave a signal at –
0.90 ppm (20 °C). Thus, the shift of the signal was not ef-
fected by the existence of THF. It shows that THT coordi-
nate 1 more effectively than THF.
dobutyl ester, as acyl chlorides react faster with THF than
1 in THF (Scheme 1).3 An appropriate solvent, activating
1 will proceed the reaction of 1,3-diketone formation.
Among the examined solvents, tetrahydrothiophene
(THT) showed the reasonable activation and characteris-
tic function for the stabilization of 1.
Scheme 1
To the dizinc reagent 1 in THF (2.0 mmol, 0.4 M), pre-
pared from diiodomethane with zinc in THF according to
the reported procedure,1e,f was added 5 ml of tetrahy-
drothiophene (THT)4 at 25 °C. The mixture was stirred for
10 min. At the same temperature, benzoyl chloride (2.0
mmol) in THF (1.0 ml) was added dropwise. The resulting
solution was stirred for 2 h at the same temperature. An
aqueous work-up afforded 1,3-diketone 3a in 98% yield,
and the formation of 2a was not observed. The results us-
ing various acyl chlorides are shown in Table 1.
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1472
S. Matsubara et al.
LETTER
The aliphatic carboxylic acid chloride was also treated The structural study about gem-dizinc compound in sol-
with 1 in THT as shown in Scheme 3. In this case, 1,3- vent has just begun and is now undergoing. But, a reason-
diketone was obtained along with the formation of vinyl able activation of 1 by adding THT make the 1,3-diketone
ester.
preparation from acyl chloride possible and effect also to
the structure of 1 in solution.
We thank Prof. Satohiro Yoshida, Dr. Tsunehiro Tanaka,
and Mr. Takashi Yamamoto (Department of Molecular
Engineering, Graduate School of Engineering, Kyoto
University) for the EXAFS measurement at Spring 8 and
helpful discussions. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas
(No.10132227 and 10208208), from The Ministry of Ed-
ucation, Science, Sports, and Culture.
Scheme 3
The difference of reactivity depending on the solvent can
be explained by a coordination to zinc, which may lead to
the change of the reagent structure itself. The possibility
of a contribution of Schlenk equilibrium should be consid-
ered (Scheme 4). The equilibrium would not be discussed
not only by eq 1 in Scheme 4 but also by eq 2, as the di-
metallic structure of 1 induces polymeric structure like
IZn–(–CH2Zn–)n–I (5) or cyclic compound 6. A removal
of solvent from a THF solution of 1 gave a white solid as
described above. The solid would not dissolve into THF
or THT. A treatment of benzoyl chloride with a THT dis-
persion of the solid gave a THF derivative 2a, and did not
afford 1,3-diketone 3a. A concentration in vacuo could
not remove THF which coordinates to 1 unless THT was
added. The solid can undergo methylenation of aldehyde
even though it was reacted as a THF dispersion. Various
References and Notes
(1) a) Marek, I.; Normant, J.-F.Chem. Rev. 1996, 96, 3241.
b) Knochel, P.; Normant, J.-F. Tetrahedron Lett. 1986, 27,
4427 and 4431. c) Nakamura, E.; Kubota, K.; Sakata, G. J.
Am. Chem. Soc. 1997, 119, 5457. d) Bertini, F.; Grasselli, P.;
Zubiani, G.; Cainelli, G. Tetrahedron 1970, 26, 1281; van de
Heisteeg, B.J.J.; Schat, M.A.; Tinga, G.; Akkerman, O.S.;
Bickelhaupt, F. Tetrahedron Lett. 1986, 27, 6123. e) Takai,
K.; Kakiuchi, T.; Utimoto, K. J. Org. Chem. 1994, 59, 2671.
f) Matsubara, S.; Mizuno, T.; Otake, Y.; Kobara, M.; Utimoto,
K.; Takai, K. Synlett 1998, 1369. g) Utimoto, K.; Toda, N.;
Mizuno, T.; Kobata, M.; Matsubara, S. Angew. Chem. Int. Ed.
Engl. 1997, 36, 2804. h) Matsubara, S.; Otake, Y.; Morikawa,
T.; Utimoto, K. Synlett 1998, 1315.
(2) Matsubara, S.; Kawamoto, K.; Utimoto, K. Synlett 1998, 267.
(3) Zinc(II) halide containing the reagent may assists the ring
opening of THF as Lewis acid. In reference 2, the preparation
of 1,3-diketone in the presence of Pd catalyst is shown.
(4) Freshly distilled Tetrahydrothiophene (drying over LiAlH4
under an Ar atmosphere) was used; bp. 119 °C. A reaction of
CH2I2, PbCl2, and Zn in THT did not afford 1. Other solvents,
such as ether, DME, and 1,4-dioxane were also examined as a
solvent for the preparation of 1. Only the reaction in 1,4-
dioxane afforded 1 in 8% yield, and the reactoins in ether and
DME did not give 1.
other solvents, DMI, CS , 1,2-dichloroethane, pyridine,
2
DMF, and DMSO, were examined to dissolve the solid.
Among them, DMSO showed a reasonable solubility. A
spectra of 1H NMR of its DMSO solution showed a sharp
singlet at –1.8 ppm. The solid was considered to be a poly-
meric dizinc species (5 or 6). The solid was also obtained
by heating 1 in THF at 80 °C for 5 h. A removal of solvent
from 1 in THF-THT gave also the white solid. The solid
is soluble in THF and THT; 1H NMR spectra of its THF
solution showed a methylene signal at –0.90 ppm (20 °C)
that is identified with 1 in THT. So an addition of THT
stabilize the structure of 1. An extended X-ray absorption
fine structure (EXAFS) spectroscopy of these reagent was
measured to get any information about structure.6,7 This
measurement showed 1 in THT exists with keeping the
high homogeneity. The Schlenk equilibrium of 1 in THT
may incline to CH2(ZnI)2 in eq 1 (Scheme 4).
(5) A measurement of 1H nmr of reagent did not show the signal
from the proton based on THF.
(6) A Structural study of organozincate by EXAFS: Uchiyama,
M.; Kameda, M.; Mishima, O.; Yokoyama, N.; Koike, M.;
Kondo, Y.; Sakamoto, T. J. Am. Chem. Soc., 1998, 120, 4943.
(7) In Figure 1 and 2, (I) EXAFS spectra of 1 in THF, (II) the
DMSO solution of the residue obtained by a removal of THF
from 1 in THF, and (III) 1 in THT, are shown. Comparison of
spectrum implies the species in is much more homogenic than
(I) and (II). So in (III) the dimetal species takes a simple
structure like CH2(ZnI)2 in a momomeric form.
Scheme 4
Synlett 1999, No. 9, 1471–1473 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Structure and Reactivity of Bis(iodozincio)methane in Tetrahydrothiophene
1473
k3-Weighted EXAFS spectra at Zn K-edge; (I) 1 in THF (0.1 M), (II)
5 in DMSO (0.1 M), and (III) 1 in THT (0.1 M).
Fourier transform of the EXAFS spectra of (I) 1 in THF (0.1 M), (II)
5 in DMSO (0.1 M), and (III) 1 in THT (0.1 M).
Figure 1
Figure 2
Article Identifier:
1437-2096,E;1999,0,09,1471,1473,ftx,en;Y13799ST.pdf
Synlett 1999, No. 9, 1471–1473 ISSN 0936-5214 © Thieme Stuttgart · New York