Generation of a low-valent titanium species from titanatrane and its catalytic reactions: Radical ring opening of oxetanes

Article abstract of DOI:10.1002/adsc.201300368

Treatment of a titanatrane complex with trimethylsilyl chloride and magnesium powder in tetrahydrofuran generated a low-valent titanium species. This species catalyzed the radical ring opening of epoxides and oxetanes to produce the corresponding less substituted alcohols. The reagent also catalyzed the deallylation and depropargylation of allylic and propargylic ethers, respectively, to provide the parent alcohols.

Full text of DOI:10.1002/adsc.201300368

COMMUNICATIONS
DOI: 10.1002/adsc.201300368
Generation of a Low-Valent Titanium Species from Titanatrane
and its Catalytic Reactions: Radical Ring Opening of Oxetanes
a
a
a
a,
Naoto Takekoshi, Kenji Miyashita, Noriaki Shoji, and Sentaro Okamoto *
a
Department of Material and Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama
221-8686, Japan
Fax : (+81)-45-413-9770; phone: (+81)-45-481-5661; e-mail: okamos10@kanagawa-u.ac.jp
Received: April 30, 2013; Revised: June 11, 2013; Published online: August 9, 2013
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300368.
Abstract: Treatment of a titanatrane complex with
trimethylsilyl chloride and magnesium powder in
tetrahydrofuran generated a low-valent titanium
species. This species catalyzed the radical ring open-
ing of epoxides and oxetanes to produce the corre-
sponding less substituted alcohols. The reagent also
catalyzed the deallylation and depropargylation of
allylic and propargylic ethers, respectively, to pro-
vide the parent alcohols.
parent alcohols. The intermolecular and intramolecu-
lar [2+2+2]cycloaddition of alkynes to substituted
benzenes could be also catalyzed by the reagent. The
McMurry coupling (olefination) reaction of aryl alde-
hydes and imino-pinacol coupling under mild homo-
geneous conditions have also been mediated by an
LVT. Recently, we found that the reagent cleaved the
NÀS or OÀS bond of sulfonamides and sulfonyl esters
to give the corresponding amines and alcohols, re-
spectively. The reagent could regioselectively cleave
the CÀO bond of epoxides to provide less substituted
Keywords: homogeneous catalysis; low-valent tita-
nium; oxetanes; radical reactions; reduction; regio-
selectivity; tripodal ligands
alcohols.
Recently, amine triphenolate metal complexes [tripo-
dal aminetris(aryloxide) complexes] have attracted
significant attention for their synthesis, structure, and
[
1]
use in catalytic reactions. The titanium complexes
titanatranes), one of the most investigated classes of
(
complexes, are characterized by a propeller-like ar-
rangement of the ligand around the titanium when
viewed along the titanium–nitrogen axis. These com-
plexes have been used as Lewis acid catalysts for lac-
[3]
[
2]
tide polymerization and aza-Diels–Alder reactions
[
4]
and for oxidations of amines and sulfides. The C3-
chiral complexes have been used as a chiral shift
[
5]
agent for NMR analysis and as an asymmetric oxi-
[6]
dation catalyst. Here we report the first examples of
the use of a titanatrane complex as a precursor for
a low-valent titanium (LVT) catalyst and its applica-
[
7]
tion in organic transformations.
Previously, we had developed a new, mild method
[
8,9]
for the generation of an LVT
Ti(O-i-Pr) , Me SiCl (or MgCl ), and Mg powder in
THF (Scheme 1). Thus, the LVT reagent catalyzed
species by using
ACHTUNGTRENNUNG
4
3
2
Scheme 1. Postulated mechanism for the generation of an
[10]
LVT from Ti ACHTGNUTRNEUNG( O-i-Pr) /Me SiCl/Mg and a proposal for the se-
4 3
the deallylation and depropargylation of allylic and lective formation of a Ti
ACHTUNGTRENNUNG
propargylic ethers, respectively, to the corresponding 1.
Adv. Synth. Catal. 2013, 355, 2151 – 2157
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2151

Naoto Takekoshi et al.
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[a]
Table 1. Ti
ACHTUNGTRENNUNG( O-i-Pr) - or complex 1-catalyzed reactions of various substrates.
4
Run Ti complex (equiv.)
Substrate
Time [h] Product(s)
12
Yield
[10b]
1
Ti
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) (1.2)
76% (98:2:0)
4
2
3
4
Ti(O-i-Pr) (0.05)
1 (0.05)
1 (0.05)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
3
12
12
12
4a+4b
4a+4b+4c
4a+4b+4c
24% (98:2:0) (64% recovered)
50% (76:10:14)
87% (75:20:5)
4
[b]
3+CHD (10 equiv.)
[
10a]
5
6
Ti
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) (0.05)
12
12
95%
>99%
4
1 (0.05)
5a
5b
6
6
6
[10a]
7
Ti
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) (0.05)
12
95%
4
8
9
1 (0.05)
1 (0.05)
12
12
>99%
92%
[10a]
10
Ti
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) (0.2)
24
60% (8 was not recovered)
4
1
1
2
1 (0.05)
8
24
12
9
5% (95% of 8 was recovered)
1
Ti
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) (1.2)
84%
4
13
14
15
16
Ti
1 (0.05)
1 (0.05)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) (0.1)
10a
10a
12
12
12
24
11a
11a
11a
no reaction
78%
66%
91%
4
[b]
10a+CHD (10 equiv.)
[b]
[
c]
Cp TiCl (2)+Mn (5) 10a+CHD (10 equiv.)
2
2
[
a]
All reactions were performed with a Ti complex, Me SiCl and Mg powder (2–3 equiv.) in THF at 40–508C. For runs 1–4
3
and 12–16, 1.2 equiv. of Me SiCl were used, for runs 5–9, 0.15 equiv. was used, and for runs 10 and 11, 1.0 equiv. was used.
3
For runs 1–15, the reactions did not proceed in the absence of a titanium compound.
[
[
b]
1,4-Cyclohexadiene.
c]
We checked the reaction of a mixture of 10a and 1,2-epoxyoctane with a Cp TiCl /Mn/CHD reagent in THF in another
2
2
vessel and found that the epoxide was converted to 1-octanol (42% yield), but 10a was recovered (98%).
For these reactions, we assume that the LVT can be species and catalyzed several reactions. In addition,
generated from Ti(O-i-Pr) , Me SiCl and Mg by during these studies, we found that LVT alkoxides cat-
a mechanism illustrated in Scheme 1: Ti
reacts with Me SiCl to yield ClTi(O-i-Pr) (A), which
AHCTUNGTRENNUNG
4
3
A
H
U
G
R
N
N
(O-i-Pr)
alyzed the radical ring-opening reaction of oxetanes.
Table 1 summarizes and compares the results of the
4
AHCTUNGTRENNUNG
3
3
can be reduced by the reaction with Mg powder to reactions of various substrates with titanium complex
generate Ti(O-i-Pr) (B) and/or its equivalents (the Ti(O-i-Pr) or 1 in the presence of Me SiCl and Mg
polymeric and/or solvated compounds). Repeating powder in THF.
a similar process might give an LVT species such as The reaction of epoxide 3 with a stoichiometric
Ti(II), Ti(I), and Ti(0). We anticipated that a Ti(III) amount of Ti(O-i-Pr) selectively gave less substituted
trialkoxide (iii) could be selectively generated when alcohol 4a in good yield (run 1);
titanium alkoxide (i) derived from an appropriate catalytic use of titanium (5 mol%) resulted in lower
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
3
4
3
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
4
[
10b,12]
however, the
[
11]
triol, such as a titanatrane complex 1, was used in- conversion (run 2). On the other hand, complex
stead of Ti(O-i-Pr) . It can be expected that steric 1 (5 mol%) could catalyze the reduction of epoxide 3,
shielding by ortho-methyl substituents in titanatrane but in lower conversion and with lower selectivity,
may prevent over-reduction through further O–Cl where the deoxygenation product 4c was co-produced
exchange of 2. (run 3). In the Ti(O-i-Pr) -promoted reactions, we re-
ACHTUNGTRENNUNG
4
1
AHCTUNGTRENNUNG
4
With this idea in mind, reactions of complex 1 with ported that the b-titanoxy radical intermediate iv in-
various substrates in the presence of Me SiCl and Mg tramolecularly abstracts a hydrogen from the i-Pr
3
[
10b]
were investigated. We found that complex 1 reacted group of the titanium complex (Figure 1).
Howev-
with Me SiCl/Mg to generate the corresponding LVT er, complex 1 has no hydrogen at the titanium b posi-
3
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Generation of a Low-Valent Titanium Species from Titanatrane and its Catalytic Reactions
However, when comparing with the ring opening of
epoxides, the ring opening of oxetanes is much slower
because of the reduced ring strain of their larger ring
[
15]
size.
Nevertheless, several examples of oxetane
cleavage have been demonstrated. Oxetane ring-
opening mediated by an organolithium species (4,4’-
di-tert-butylbiphenylide) has been developed by
Cohen et al. where the regiochemistry of the CÀO
Figure 1. Hydrogen abstraction by b-titanoxy radicals.
bond cleavage changes in the presence of a Lewis
[
16]
tion; therefore, in the 1-catalyzed reaction, the tita- acid such as AlEt3.
Thus, in the absence of any
noxy radical intermediate v intermolecularly abstracts Lewis acid the CÀO bond cleavage occurs at the less
a hydrogen from a solvent (THF) or undergoes deox- substituted carbon for the alkyl-substituted oxetane-
[
16a]
ygenation through a b-titanoxy alkyltitanium inter- s.
mediate. When excess of 1,4-cyclohexadiene (CHD) cleavage occurs at the more substituted carbon.
In contrast, in the presence of AlEt CÀO bond
3
[16b]
was used as a hydrogen source in the 1-catalyzed re- These reactions yield the corresponding g-lithioalkox-
action, a higher yield of the alcohols 4a and 4b was at- ides, which can be utilized as nucleophiles and for
tained (run 4).
transmetallation to cerium and chromium deriva-
[17]
Both titanium complexes Ti
A
H
U
G
R
N
U
G
Recently, Gansꢁuer, Grimme et al. reported
4
catalyzed the deallylation of allylic ethers 5a and 5c the reductive opening of oxetanes promoted by
and the depropargylation of propargylic ether 5b to a Cp TiCl reagent, the reaction of which proceeds by
2
quantitatively give the corresponding alcohol (runs 5– a radical reaction pathway. Calculation results sug-
9
). By contrast, complex 1 exhibited marginal activity gested that non- or mono-substituted oxetanes at the
for the cyclotrimerization of triyne 8 (run 11), but 2 position might be barely cleaved under these condi-
Ti(O-i-Pr) catalyzed the reaction (run 10). These re- tions, thereby limiting the reaction to 2,2-disubstituted
sults allow us to conclude that the reaction of com- oxetanes.
plex 1 with Me SiCl and Mg generated the corre- The results shown in Table 1 prompted us to inves-
sponding LVT species that have distinct reactivities tigate the Ti(O-i-Pr) - and 1-catalyzed reductions of
from Ti(O-i-Pr) . To the best of our knowledge, these oxetanes (Scheme 3) because of their higher reducing
ACHTUNGTRENNUNG
4
[
13]
3
AHCTUNGTRENNUNG
4
ACHTUNGTRENNUNG
4
are the first examples of the use of complex 1 as a pre-
cursor for an LVT catalyst.
In addition to the aforementioned reactions, we
found that LVT alkoxides could reduce oxetanes to
the corresponding alcohols (runs 12–15). Thus, a stoi-
chiometric or catalytic amount of Ti ACHTUNGTERNN(UNG O-i-Pr) with
4
Me SiCl and Mg reduced oxetane 10a to primary al-
3
cohol 11a in good yield (runs 12 and 13, respectively).
Similarly, complex 1 catalyzed the reduction of 10a,
and a high yield was attained when excess CHD was
used (runs 14 and 15). This high yield was attributed
Scheme 3. Complex-1 catalyzed reduction of oxetanes 10 to
alcohols 11.
to a higher reagent potential for reduction compared potency than a Cp TiCl reagent. The results of the re-
2
with cyclopentadienyl (Cp)-based reagents such as action of representative oxetanes 10b–10j are sum-
Cp TiCl and its dimer because the Cp TiCl /Mn/CHD marized in Table 2.
2
2
2
[
13]
reagent did not react with oxetane 10a (run 16).
As revealed from Table 2, the present method
Since oxetanes 10 are readily available from epox- could indeed reduce non- and mono-substituted oxe-
ides or carbonyl compounds by a one-step reaction tanes at the 2 position; therefore, it is more general in
+
À
[14]
with Me S (=O)CH reagent, their reduction to al- terms of the substrate structure than the Cp TiCl-pro-
2
2
2
cohols 11 may be synthetically versatile as a formal moted reaction. In addition to 10a (Table 1), 3,3-di-
one- or two-carbon homologation reaction substituted oxetanes 10b and 10c were cleanly re-
Scheme 2).
AHCTUNGTRENNUNG
(
duced to the corresponding alcohols 11b and 11c, re-
spectively, without any loss of benzyloxy and silyloxy
functionalities (runs 1 and 2 in Table 2). The ring
opening reactions of 2-mono-aryl- and mono-alkyl-
[
18]
[19]
substituted oxetanes 10d
and 10e
occurred
smoothly at the 2 position to give the corresponding
primary alcohol (runs 3–8). 2,2-Disubstitued oxetanes
1
0f and 10g and spiro compounds 10h and 10i were
Scheme 2. Formal one- or two-carbon homologation.
also reduced to the corresponding primary alcohol
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Naoto Takekoshi et al.
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Table 2. Reductive ring-opening reactions of oxetanes 10 catalyzed by a complex 1/Me SiCl/Mg reagent.
3
[a]
Run Oxetane 10
10
Ti complex Time Product(s)
h]
Yield
76%
[
[b]
1
10b 1+CHD
12
[b]
2
3
10c
10d
1+CHD
12
12
58%
62%
1
[
b]
4
5
10d 1+CHD
10d Ti
12
12
11d
11d
74%
72%
[
[
c]
c]
A
T
N
T
E
N
G
4
6
10e
1
12
90%
[b]
7
8
10e
10e
1+CHD
Ti
12
12
11e
11e
99%
61%
ACHTUNGTRENUNNG( O-i-Pr)
4
total 65%
9
10f
1
12
(
11f:11f’=92:8)
[
b]
1
1
0
1
10f
10f
1+CHD
Ti(O-i-Pr)
12
12
11f
11f
80%
81%
[c]
AHCTUNGTRENNUNG
4
[b]
1
2
10g
10h
1+CHD
12
98%
[d]
total >99%
[d]
1
3
1
24
(
11h:11h’=74:26)
[
b]
[d]
1
1
4
5
10h 1+CHD
10h Ti(O-i-Pr)
24
24
11h
11h
89%
[e]
A
H
U
G
R
N
U
G
45% (80% conver-
4
[d]
sion)
total 96%
16
10i
1
24
(11i:11i’=73:27), dr
of 11i= >99:1
[b]
1
7
8
10i
10j
1+CHD
1
24
24
11i
96%, dr>99:1
total 81%
1
(
11j:11j’=60:40)
[
b]
1
2
2
9
0
1
10j
10j
10j
1+CHD
24
24
60
11j+11j’
11j+11j’
11j+11j’
total 99%
11j:11j’=70:30)
(
[
[
e]
g]
[f]
Ti
Ti
A
H
U
G
R
N
U
G
total 19%
11j:11j’=61:39)
total 99%
11j:11j’=58:42)
4
(
AHCTUNGTREUNNNG( O-i-Pr)
4
(
[
[
[
[
[
[
[
a]
Unless otherwise indicated, 5 mol% of a titanium complex, 1.2 equiv. of Me SiCl, and 3.0 equiv. of Mg powder were used.
3
b]
1
0
0 equiv. of 1,4-cyclohexadiene were used.
.1 equiv. of Ti(O-i-Pr) was used.
c]
d]
e]
f]
ACHTUNGTRENNUNG
4
A mixture of diastereomers. Ratio of cis:trans was 70:30, 88:12, or 69:31 for run 13, 14, or 16, respectively.
1
7
1
.2 equiv. of Ti
8% of 10j were recovered.
.2 equiv. of Ti
ACHTUNGTRENNUNG( O-i-Pr) were used.
4
g]
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(O-i-Pr) and 3.0 equiv. of Me SiCl were used.
4
3
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Adv. Synth. Catal. 2013, 355, 2151 – 2157

Generation of a Low-Valent Titanium Species from Titanatrane and its Catalytic Reactions
(
runs 9–17), where the presence of excess CHD as g-titanoxy radical H can abstract hydrogen from 1,4-
a hydrogen source prevented the formation of the cyclohexadiene (or solvent THF). The reaction of the
alkene by-product. It is noteworthy that the product resulting titanium alkoxide I with silyl chloride trans-
1
1i was quantitatively obtained as a single diastereo- forms I to the titanium chloride complex E. The re-
[20]
mer by the reduction of 10i, due to the selective hy- gioselectivity of the ring-opening reaction, which gen-
drogen abstraction from the less hindered face of the erally gives less substituted alcohols, can be explained
intermediate g-titanoxy radical (run 17). As shown in by assuming the stability of the g-titanoxy radical in-
runs 18 and 19, the 1-catalyzed reduction of bicyclic termediate H against J. However, as can be seen in
oxetane 10j derived from d- xylose smoothly pro- the reduction of 10j (runs 18–21 of Table 2) one may
ceeded and yielded 3-deoxyribose ketal 11j as also be required to consider another factor such as
[21]
[
22]
a major product, but a large amount of 5-deoxy- a kinetic effect arising from the independent sub-
xylose ketal 11j’ was co-produced. The presence of strate structure. The mechanism for the formation of
CHD led a better selectivity (run 19). Since the Ti ACHUTNGRNEUNG( O- the alkene by-product observed in several reactions is
i-Pr) -based reaction was comparably slow, a stoichio- unclear. It is most likely due to a hydrogen atom ab-
4
metric amount of titanium with a longer reaction time straction from a radical by a radical (radical dispro-
[
23]
was required for completion (runs 20 and 21). These portionation). Alternatively, it can be produced via
results of regioselectivity were slightly disappointing, a cationic intermediate K generated by activation
because we anticipated a higher selectivity consider- with a Lewis acid such as titanium or a magnesium
ing the stability of the corresponding g-titanoxy radi- salt.
cal intermediates. The rationalization of the results
must await further study.
We have demonstrated that the treatment of a tita-
natrane complex 1 with Me SiCl and Mg powder in
3
In Scheme 4, we propose the reaction mechanism THF generated a low-valent titanium species. This
for the 1-catalyzed reduction of oxetanes. Complex species catalyzed the deallylation of allylic ethers, the
1
can be converted to its chloride E by reaction with depropargylation of propargylic ethers, and the radi-
silyl chloride, which may immediately be reduced by cal ring-opening reaction of epoxides and oxetanes.
Mg powder to generate a Ti(III) complex F. Complex The reductive ring-opening reaction of epoxides and
AHCTUNGTRENNUNG
F forms G by the coordination of an oxetane oxygen, oxetanes gave the corresponding less substituted alco-
followed by a single electron transfer. The generated hols as major product. The Ti-catalyzed CÀO bond
cleavage of non- or mono-substituted oxetanes at the
2
position was achieved for the first time by the pres-
ent low-valent titanium alkoxides.
The LVT derived from titanatrane 1 is a stronger
reductant and more reactive than a Cp TiCl reagent
2
but, therefore, less chemoselective. As a result, both
reagents may complementarily be used.
Experimental Section
General
1
NMR spectra were recorded in CDCl at 500 MHz for H
3
1
3
and 125 MHz for C, respectively. Chemical shifts are re-
ported in parts per million (ppm, d) relative to Me Si (d=
4
1
0
.00), residual CHCl (d=7.26 for H NMR), or a center
peak of CDCl (d=77.0 for C NMR). IR spectra were re-
3
1
3
3
corded on an FT-IR spectrometer (JASCO FTIR-4100).
High-resolution mass spectra (HR-MS) were measured on
a JEOL Accu TOF T-100 system equipped with ESI ioniza-
tion. All reactions sensitive to oxygen and/or moisture were
performed under an argon atmosphere. Dry solvents were
purchased from Kanto Chemical Co., Inc. and were used as
received. Ti
ACHTUNGTNERNGNU( O-i-Pr) was distilled and stored under an argon
4
atmosphere. Me SiCl was stored over CaH to remove HCl.
3
2
Room temperature refers to 20–258C. Titanium complex
[
11]
1
was synthesized according to the reported procedures.
[17] [18] [19] [13] [13]
Scheme 4. Proposed mechanism for 1-catalyzed reduction
with oxetanes.
Oxetane substrates 10b,
10h, 10i, and 10j were respectively prepared accord-
10d,
10e,
10f,
10g,
[13]
[20]
[21]
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Naoto Takekoshi et al.
COMMUNICATIONS
ing to the reported procedures. Oxetane 10a was a gift from
Toagosei Co., Ltd.
17-vinyl-7,8,9,11,12,13,14,15,16,17-decahydro-6H-cyclopen-
[33]
ta[a]phenanthrene (12)
by bromination of the alcohol
with subsequent dehydrohalogenation and the comparison
[33]
of the spectral data with reported data.
tert-Butyldimethyl[(3-methyloxetan-3-yl)methoxy]-
silane (10c)
Silane 10c (907 mg) was prepared from (3-methyloxetan-3-
yl)methanol (510 mg, 5.0 mmol) by the reaction with imida-
zole (748 mg, 11 mmol) and t-BuMe SiCl (904 mg,
2
6
.0 mmol) in DMF (10 mL) at room temperature for 12 h;
1
yield: 84%. H NMR: d=4.49 (d, J=5.2 Hz, 2H) 4.32 (d,
J=5.8 Hz, 2H) 3.63 (s, 2H) 1.27 (s, 3H) 0.90 (s, 9H) 0.06 (s,
6
13
H); C NMR: d=9.6, 68.1, 40.9, 25.8, 18.3, À5.5; IR
À1
(
neat): n=2950, 2930, 2986, 1472, 1464, 1387, 1256 cm ;
+
HR-MS: m/z=255.1185, calcd. for C H KO Si [M+K] : Acknowledgements
1
1
24
2
255.1183.
We thank the Scientific Frontier Research Project from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy (MEXT), Japan, for financial support.
General Procedure for Reductive Cleavage of
Oxetanes Catalyzed by Complex 1 with Me SiCl and
3
Mg powder (Table 2)
Under an argon atmosphere, to a mixture of an oxetane 10 References
1.00 mmol), Mg powder (73 mg, 3.0 mmol), complex
(
1
1
1
(26.9 mg, 0.05 mmol), and 1,4-cyclohexadiene (0 or
[1] G. Licini, M. Mba, C. Zonta, Dalton Trans. 2009, 5265–
5277.
0 mmol) in THF (5 mL) was added Me SiCl (0.15 mL,
3
.2 mmol) at room temperature. The resulting mixture was
[2] Y. Kim, J. G. Verkade, Macromolecules 2002, 35, 2395–
2399; Y. Kim, G. K. Jnaneshwara, J. G. Verkade, Inorg.
Chem. 2003, 42, 1437–1447; S. Gendler, S. Segal, I.
Goldberg, Z. Goldschmidt, M. Kol, Inorg. Chem. 2006,
45, 4783–4790.
[3] S. T. Bull, M. G. Davidson, A. L. Johnson, M. F.
Mahon, D. E. J. E. Robinson, Chem. Asian J. 2010, 5,
612–620.
[4] M. Mba, L. J. Prins, G. Licini, Org. Lett. 2007, 9, 21–24;
C. Zonta, E. Cazzola, M. Mba, G. Licini, Adv. Synth.
Catal. 2008, 350, 2503–2506; M. Mba, L. J. Prins, C.
Zonta, M. Cametti, A. Valkonen, K. Rissanen, G.
Licini, Dalton Trans. 2010, 39, 7384–7392.
stirred for 12–24 h (confirming the completion of the reac-
tion by thin layer chromatography) at 40–508C. After addi-
tion of saturated aqueous NaHCO (5 mL), the mixture was
extracted with ethyl acetate. The organic layer(s) was
washed with aqueous 0.1M HCl and then saturated aqueous
NaHCO , dried over MgSO , filtered, concentrated under
reduced pressure. The residue was purified by column chro-
matography on silica gel with appropriate solvents (hexane/
ether or hexane/ethyl acetate) to yield the ring-opening
product 11.
3
3
4
[
24]
[25]
[26]
[27]
The structures of the products 9, 11b, 11c, 11d,
[28]
[29]
[13]
[30]
[31]
[32]
11e,
11f,
11g,
11h,
11j,
and 11j’
were con-
firmed by the comparison of their spectroscopic data with
[5] C. Zonta, A. Kolarovic, M. Mba, M. Pontini, E. P.
Kꢂndig, G. Licini, Chirality 2011, 23, 796–800.
[6] P. Axe, S. D. Bull, M. G. Davidson, M. D. Jones,
D. E. J. E. Robinson, W. L. Mitchell, J. E. Warren,
Dalton Trans. 2009, 10169–10171.
those reported.
1
2-Methyl-2-(phenoxymethyl)butan-1-ol (11a): H NMR:
d=7.28 (t, J=6.6 Hz, 2H), 6.95 (t J=6 Hz, 1H), 6.91 (d, J=
6
1
1
.3 Hz, 2H), 3.82 (d, J=7.5 Hz, 1H), 3.78 (d, J=7.5 Hz,
H), 3.60 (dd, J=5.2, 9.2 Hz, 1H), 3.57 (d, J=5.2, 9.2 Hz,
H), 1.96 (t, J=4.9 Hz, 1H), 1.49 (q, J=6.3 Hz, 2H), 0.95
[7] For the redox behaviour of amine triphenolate titanium
complexes, see: D. Lionetti, A. J. Medvecz, V. Ugrino-
va, M. Quiroz-Guzman, B. C. Noll, S. N. Brown, Inorg.
Chem. 2010, 49, 4687–4697. Dimer of 2 was synthesized
by the reaction of 1 with BH and PMe and character-
1
3
(
s, 3H), 0.90 (t, J=6.3 Hz, 3H); C NMR: d=158.9, 129.4,
1
3
20.9, 114.5, 73.6, 68.6, 38.8, 26.6, 18.3, 7.6; IR (neat): n=
À1
353, 2961, 2930, 1600, 1496, 1471, 1248, 1300 cm ; HR-MS:
3
3
+
m/z=217.1204, calcd. for C H NaO [M+Na] : 217.1199.
ized by single crystal X-ray diffraction: A. L. Johnson,
M. G. Davidson, M. F. Mahon, Dalton Trans. 2007,
5405–5411.
1
2
18
2
2
-[(8S,9S,13R,14S,17R)-3-Methoxy-13-methyl-
7
,8,9,11,12,13,14,15,16,17-decahydro-6H-cyclopenta[a]phen-
anthren-17-yl]ethanol (11i): H NMR: d=7.25 (s, 1H), 7.21
d, J=8.6 Hz, 1H), 6.71 (dd, J=2.9, 8.6 Hz, 1H) 6.63 (d, J=
1
[8] a) J. E. McMurry, Acc. Chem. Res. 1974, 7, 281–286;
b) J. E. McMurry, Acc. Chem. Res. 1983, 16, 405–411;
c) J. E. McMurry, Chem. Rev. 1989, 89, 1513–1524;
d) D. Lenoir, Synthesis 1989, 883–897; e) B. E. Kahn,
R. D. Rieke, Chem. Rev. 1988, 88, 733–745; f) M. Eph-
ritikhine, Chem. Commun. 1998, 2549–2554; g) A.
Fꢂrstner, B. Bogdanovi, Angew. Chem. 1996, 108,
2582–2609; Angew. Chem. Int. Ed. Engl. 1996, 35,
2442–2469; h) W. A. Nugent, T. V. RajanBabu, J. Am.
Chem. Soc. 1988, 110, 8561–8562; i) T. V. RajanBabu,
W. A. Nugent, J. Am. Chem. Soc. 1989, 111, 4525–4527;
(
2
2
9
1
2
2
.9 Hz, 1H), 3.78 (s, 3H), 3.75–3.60 (m, 4H), 2.92–2.79 (m,
H), 2.35–2.15 (m, 2H), 1.95–1.75 (m, 5H), 1.49–1.21 (m,
1
3
H), 0.63 (s, 3H); C NMR: d=157.4, 138.1, 132.9, 126.3,
13.8, 111.4, 62.6, 55.2, 54.7, 47.3, 44.1, 42.5, 38.8, 37.7, 33.7,
9.9, 28.4, 27.8, 26.4, 24.4, 12.6; IR (KBr): n=3568, 2926,
À1
866, 2846, 2806, 1607, 1454, 1314 1287,1250 cm ; HR-MS:
+
m/z=315.2314, calcd. for C H O [M+H] : 315.2319.
2
1
31
2
The stereochemistry of resulting 11i was confirmed by its
conversion to the known compound 3-methoxy-13-methyl-
2156
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Adv. Synth. Catal. 2013, 355, 2151 – 2157

Generation of a Low-Valent Titanium Species from Titanatrane and its Catalytic Reactions
j) A. Gansꢁuer, H. Bluhm, Chem. Rev. 2000, 100, 2771–
[16] a) B. Mudryk, T. Cohen, J. Org. Chem. 1989, 54, 5657–
2
2
788; k) A. Gansꢁuer, S. Narayan, Adv. Synth. Catal.
002, 344, 465–475; l) J. M. Cuerva, J. Justicia, J. L.
5659; b) B. Mudryk, T. Cohen, J. Org. Chem. 1991, 56,
5760–5761.
Oller-Lꢃpez, J. E. Oltra, Top. Curr. Chem. 2006, 264,
3–92; m) X. Zheng, X.-J. Dai, H.-Q. Yuan, C.-X. Ye, J.
Ma, P.-Q. Huang, Angew. Chem. Int. Ed. 2013, 52,
494–3498, and references cited therein.
[17] E. Licandro, S. Maiorana, A. Papagni, A. Zanotti-
Gerosa, J. Chem. Soc. Chem. Commun. 1992, 1623–
1624; B. Mudryk, C. A. Shook, T. Cohen, J. Am. Chem.
Soc. 1990, 112, 6389–6391.
6
3
[
9] For low-valent titanium alkoxides, see: F. Sato, H.
Urabe, S. Okamoto, Chem. Rev. 2000, 100, 2835–2886;
O. G. Kulinkovich, A. de Meijere, Chem. Rev. 2000,
[
[
[
[
18] D. Darensboug, A. Moncada, S.-H. Wei, Macromole-
cules 2011, 44, 2568–2576.
19] D. W. Kwon, Y. H. Kim, J. Org. Chem. 2002, 67, 9488–
1
6
00, 2789–2834; J. J. Eisch, J. Organomet. Chem. 2001,
17–618, 148–157; F. Sato, S. Okamoto, Adv. Synth.
9
491.
20] S. C. Welch, A. S. C. Prakasa, J. T. Lyon, J.-M. Assercq,
J. Am. Chem. Soc. 1983, 105, 252–257.
21] O. Muraoka, K. Yoshikai, H. Takahashi, T. Minematsu,
G. Lu, G. Tanabe, T. Wang, H. Matsuda, M. Yoshikawa,
Bioorg. Med. Chem. 2006, 14, 500–509.
Catal. 2001, 343, 759–784; F. Sato, H. Urabe, S. Okamo-
to, Synlett 2000, 753–775; F. Sato, H. Urabe, in: Titani-
um and Zirconium in Organic Synthesis, (Eds.: I,
Marek), Wiley-VCH, Weinheim, Germany, 2002,
pp 319–354.
[
22] A. Gansꢁuer, A. Barchuk, F. Keller, M. Schmitt, S.
Grimme, M. Gerenkamp, C. Mꢂck-Lichtenfeld, K.
Daasbjerg, H. Svith, J. Am. Chem. Soc. 2007, 129,
[
10] a) M. Ohkubo, S. Mochizuki, T. Sano, Y. Kawagichi, S.
Okamoto, Org. Lett. 2007, 9, 773–776; b) T. Kawaji, N.
Shohji, K. Miyashita, S. Okamoto, Chem. Commun.
1
359–1371.
2
011, 47, 7857–7859; c) N. Shohji, T. Kawaji, S. Okamo-
[
[
[
[
[
[
[
23] J. Justicia, T. Jimenez, S. P. Morcillo, J. M. Cuerva, J. E.
Oltra, Tetrahedron 2009, 65, 10837–10841.
24] N. Saino, D. Kogure, S. Okamoto, Org. Lett. 2005, 7,
to, Org. Lett. 2011, 13, 2626–2629, and references cited
therein.
[
11] S. D. Bull, M. G. Davidson, A. L. Johnson, M. F.
3
065–3067.
25] Y. Yang, J. Wang, M. Kayser, Tetrahedron: Asymmetry
007, 18, 2021–2029.
26] S. Brandau, D. Hoppe, Tetrahedron 2005, 61, 12244–
2255.
27] G. Chen, C. Fu, S. Ma, Tetrahedron 2006, 62, 4444–
452.
Mahon, D. E. J. E. Robinson, Chem. Asian J. 2010, 5,
6
12–620; S. D. Bull, M. G. Davidson, A. L. Johnson,
D. E. J. E. Robinson, M. F. Mahon, Chem. Commun.
003, 1750–1751.
2
2
1
[
12] Cp TiCl-mediated or -catalyzed ring opening of epox-
2
ides: T. V. RajanBabu, W. A. Nugent, J. Am. Chem.
Soc. 1994, 116, 986–997; A. Gansꢁuer, H. Bluhm, M.
Pierobon, J. Am. Chem. Soc. 1998, 120, 12849–12859;
A. F. Barrero, A. Rosales, J. M. Cuerva, J. E. Oltra,
Org. Lett. 2003, 5, 1935–1938. A recent review: A. Gan-
sꢁuer, C.-A. Fan, J. Justicia, D. Worgull, Top. Curr.
Chem. 2007, 279, 25–52.
4
28] F. Tancini, T. Gottschalk, W. R. Schweizer, F. Dieder-
ich, E. Dalcanale, Chem. Eur. J. 2010, 16, 7813–7819.
29] R. Bussas, H. Mꢂnsterer, G. Kreaze, J. Org. Chem.
1983, 48, 2828–2832.
[30] G. Eadon, J. Am. Chem. Soc. 1976, 98, 7313–7319.
[31] K. Jacobson, S. M. Siddiqi, M. Olah, X. Ji, N. Melman,
K. Bellamkonda, Y. Mesgulam, G. Stiles, H. O. Kim, J.
Med. Chem. 1995, 38, 1720–1735.
[
13] A. Gansꢁuer, N. Ndene, T. Lauterbach, J. Justicia, I.
Winkler, C. Mꢂck-Lichtenfeld, S. Grimme, Tetrahedron
2
008, 64, 11839–11845.
14] K. Okuma, Y. Tanaka, S. Kaji, H. Ohta, J. Org. Chem.
983, 48, 5133–5134.
[
[
[32] P. M. Vadhadiya, V. G. Puranik, C. V. Ramana, J. Org.
1
Chem. 2012, 77, 2169–2175.
15] A. Gansꢁuer, T. Lauterbach, S. Narayan, Angew.
[33] Y. Tomono, H. Hirota, Y. Imahara, N. Fusetani, J. Nat.
Prod. 1999, 62, 1538–1541.
Chem. 2003, 115, 5714–5731; Angew. Chem. Int. Ed.
2
003, 42, 5556–5573.
Adv. Synth. Catal. 2013, 355, 2151 – 2157
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2157