Synthesis of heterodinuclear hemisalen complexes on a hexaarylbenzene scaffold and their application for the cross-pinacol coupling reaction

Article abstract of DOI:10.1002/chem.201303946

Intermolecular cross-pinacol coupling reaction between aliphatic and aromatic aldehydes by using heterodinuclear hemisalen complexes 1_cis with vanadium(V) and titanium(IV) on a hexaarylbenzene scaffold is reported. Our ligand design is based on the individual activation of two aldehydes by vanadium and titanium, which are positioned with a suitable space on the rigid scaffold. Ligands such as 1_cis were synthesized by Diels-Alder addition and decarbonylation reaction, followed by condensation of dialdehyde 3_cis with various aminophenols. The influence of the substituents on the ligands on the pinacol coupling reaction was investigated. As a result, the reductive coupling reaction between aliphatic and aromatic aldehydes by using a catalytic amount of 1_cis in the presence of Me₃SiCl and Zn provided the corresponding cross-coupled 1,2-diol in good yields with high cross-selectivity. Working together: Dihemisalen ligands on a hexaaryl benzene scaffold were designed and the heterodinuclear complexes 1_cis with vanadium(V) and titanium(IV) were synthesized from the corresponding disalicylaldehyde compound (see scheme). By using the heterodinuclear catalysts, the selective intermolecular cross-pinacol coupling reaction between aliphatic and aromatic aldehydes is demonstrated. Copyright

Full text of DOI:10.1002/chem.201303946

DOI: 10.1002/chem.201303946
Full Paper
&
Heterometallic Complexes
Synthesis of Heterodinuclear Hemisalen Complexes on
a Hexaarylbenzene Scaffold and their Application for the Cross-
Pinacol Coupling Reaction
Akihiro Miyasaka,[a] Toru Amaya,[a] and Toshikazu Hirao*[a, b]
Abstract: Intermolecular cross-pinacol coupling reaction be-
tween aliphatic and aromatic aldehydes by using heterodi-
nuclear hemisalen complexes 1cis with vanadium(V) and tita-
nium(IV) on a hexaarylbenzene scaffold is reported. Our
ligand design is based on the individual activation of two al-
dehydes by vanadium and titanium, which are positioned
with a suitable space on the rigid scaffold. Ligands such as
lation reaction, followed by condensation of dialdehyde 3cis
with various aminophenols. The influence of the substitu-
ents on the ligands on the pinacol coupling reaction was in-
vestigated. As a result, the reductive coupling reaction be-
tween aliphatic and aromatic aldehydes by using a catalytic
amount of 1cis in the presence of Me3SiCl and Zn provided
the corresponding cross-coupled 1,2-diol in good yields with
high cross-selectivity.
1cis were synthesized by Diels–Alder addition and decarbony-
Introduction
a challenging issue due to the difficulty of discriminating be-
tween the two aldehydes in the reaction. So far, there are only
a few examples for the cross-pinacol-type coupling, which
strongly depend on the combination of substrates.[5] For exam-
ple, Pedersen et al. reported the cross-pinacol coupling reac-
tions with stoichiometric dimeric vanadium complex between
aldehydes containing an appropriately placed chelating group
and aliphatic aldehydes.[5b–f] Takai et al. showed that the reac-
tion of a,b-unsaturated ketone treated with an excess of chro-
mium compound produces the corresponding allylic CrIII inter-
mediate. The organometallic chromium species attacks the ali-
phatic aldehyde to give the corresponding 1,2-diol.[5j] Groth
and co-workers developed the chromium-mediated cross-cou-
pling reaction of a,b-unsaturated carbonyl compounds and al-
dehydes by using a catalytic amount of chromium chloride
with a chlorosilane and a co-reductant.[5k,l] On the other hand,
catalytic cross-pinacol coupling reaction between simply sub-
stituted aromatic and aliphatic aldehydes have, to the best of
our knowledge, never been reported. Therefore, a reductant
control strategy is desired for this catalytic reaction.
The reductive coupling reactions of carbonyl compounds with
the aid of low-valent early transition-metals provide an impor-
tant method for the construction of vicinally functionalized
carbon frameworks (Scheme 1).[1] In fact, the pinacol coupling
Scheme 1. Cross-pinacol coupling reaction.
reaction has been used as key steps in the synthesis of taxol[2]
and HIV protease inhibitors.[3] Now, catalytic, diastereoselective,
and/or enantioselective methods have been developed.[1] In
our group, a catalytic system for the pinacol coupling reaction
consisting of a low-valent vanadium or titanium compound
with a chlorosilane and a co-reductant was revealed.[4] Howev-
er, the intermolecular cross-pinacol coupling reactions, which
are apparently more important than the homo-coupling reac-
tions as a tool for the convergent synthetic strategies, is still
In this context, we envisioned that the controlled arrange-
ment of two metals on a rigid scaffold could provide spatially
regulated reaction sites for the cross-pinacol coupling reaction
(Figure 1). In our previous study, the bis-biphenol ligand on
a hexaphenylbenzene scaffold was designed, and step-by-step
activation of two different aromatic aldehydes by using stoi-
chiometric dititanium complexes increased the cross-selectivi-
ty.[6] Further increase of cross-selectivity is expected by the in-
troduction of heterobimetals to the ligand because the reactiv-
ity of substrates strongly depends on the metal in the pinacol
coupling reaction. For example, low-valent vanadium on Schiff
base complexes activates aromatic aldehydes,[7a] but does not
activate aliphatic aldehydes.[7b] In contrast, low-valent titanium
activates both aliphatic and aromatic aldehydes.[7c–e] Therefore,
[a] A. Miyasaka, Dr. T. Amaya, Prof. T. Hirao
Department of Applied Chemistry
Graduate School of Engineering, Osaka University
Yamada-oka, Suita, Osaka 565-0871 (Japan)
Fax: (+81)6-6879-7415
E-mail: hirao@chem.eng.osaka-u.ac.jp
[b] Prof. T. Hirao
JST, ACT-C
4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303946.
Chem. Eur. J. 2014, 20, 1615 – 1621
1615
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Figure 1. Concept for cross-pinacol coupling reaction with ligand controlled
dual activation.
Scheme 2. Synthetic strategy for heterodinuclear complex 1cis
.
a heterobimetallic complex in which two discriminated sites
are three-dimensionally regulated through a suitable spacer
unit would lead to multifunctional catalysts with individually
activated sites (Figure 1). We have already demonstrated the
synthesis of desymmetrized dinuclear vanadium(V) complexes
from the disalicylaldehyde compound on a hexaarylbenzene
scaffold.[8] These complexes have two different substituents (R5
and R6) around each metal, which are expected to directly in-
teract with substrates based on steric repulsion, p-p interac-
tion, or hydrophobic interaction because the bulky hexaaryl-
benzene scaffold is located on the opposite side of two sub-
stituents from activation sites. Here, we report the synthesis of
heterodihemisalen complexes 1cis, and their application for the
cross-pinacol coupling reaction between aliphatic and aromatic
aldehydes.
Results and Discussion
Our synthetic strategy for obtaining heterodinuclear catalysts
1cis is outlined in Scheme 2. Bimetallic complexes 1cis were en-
visaged to be constructed through condensation of monoalde-
hydes 2cis with various aminophenols, followed by complexa-
tion with a transition metal such as a vanadium(V) or titanu-
m(IV) compound. Monoaldehyde 2cis is similarly prepared from
the dialdehyde 3cis,[9] and dialdehyde 3cis would arise from the
Diels–Alder addition-decarbonylation reaction[10] of tolan 4
with tetraphenylcyclopentadienone (5).
The synthesis of 3 is shown in Scheme 3. 1,2-Bis(2-methoxy-
phenyl)ethyne (6)[11] was treated with BuLi, followed by trap-
ping of N,N-dimethylformamide (DMF) to give dialdehyde 4 in
52% yield. The Diels–Alder addition-decarbonylation of 4 with
cyclopentadienone 5 in Ph2O heated to reflux led to the hex-
aarylbenzene scaffold. Subsequent deprotection with BBr3
gave disalicylaldehyde 3 as a mixture of cis and trans isomers
(two steps 65%, cis/trans=22:78). The diastereomers could be
separated by silica-gel chromatography, and gram-scale syn-
Scheme 3. Synthesis and structural assignment of 3.
thesis was possible. The structural assignment of the cis/trans
isomers was made on the basis of 2D NOESY experiments on
[12]
the desymmetrized monomethoxy derivative 7cis and 7trans
.
The isomer 7cis, in which cross-peaks were observed between
the methoxy group and the hydroxyl group of another side in
a 2D NOESY spectrum, was assigned as a cis isomer. The cis/
trans determination of disalicylaldehyde 3 was carried out by
transformation from each isomer of the monomethoxy deriva-
tive 7 by deprotection (see Scheme S1 in the Supporting infor-
mation).
The cis isomer 3cis is a minor product in the Diels–Alder addi-
tion-decarbonylation reaction, however, treatment of 3trans in
anisole at 1508C for 16 h led to cis and trans isomers
Chem. Eur. J. 2014, 20, 1615 – 1621
www.chemeurj.org
1616
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Table 1. Screening of catalysts for cross-pinacol coupling reaction of 8a
and 9a.[a,b]
Entry
Catalyst
Yield [%][c,d]
10a (syn/anti) 11a 12a 10a 11a 12a
Molar ratio
1
2
3
4
5
6
1acis
1bcis
1ccis
1dcis
17 (63:37)
15 (68:32)
69 (64:36)
73 (59:41)
0
0
12
10
37
–
17
21
29
23
7
1.0
1.4
5.9
7.1
2.4
–
–
–
1
1
1
–
1
1
1.2
1.1
0.1
–
13+14[e] 88 (63:37)
none
0
–
[a] Reaction conditions (see the experimental section): 8a (0.4 mmol), 9a
(0.2 mmol), catalyst (0.01 mmol). [b] Slow addition (1 h) of 9a by using
a syringe pump. [c] Yield of 10a=(mole of 10a)/0.2 mmolꢁ100, yield of
11 a =[(mole of 11 a)ꢁ2]/0.4 mmolꢁ100, yield of 12a=[(mole of 12a)ꢁ
2]/0.2 mmolꢁ100. [d] Determined by 1H NMR spectroscopic analysis of
the crude mixture. [e] The reaction was performed by using 13
(0.01 mmol) and 14 (0.01 mmol)
Scheme 4. Synthesis of 1cis
.
(Scheme 3, cis/trans=12:88). On the other hand, this isomeri-
zation did not occur at 908C even after 24 h, indicating the
conformational rigidity.
Based on the synthetic plan shown in Scheme 2, the hetero-
dinuclear complexes 1cis were synthesized (Scheme 4). Conden-
sation of the disalicylaldehyde 3cis with 2-amino-6-tert-butyl-
phenol led to the mono- and dihemisalen ligands. The mono-
hemisalen ligand was separated by silica-gel chromatography,
then complexation with VO(OiPr)3 in ethanol/dichloromethane
solution gave mononuclear vanadium(V) complex 2acis (R5 =
tBu) in 40% yield (two steps).[13] The vanadium complex 2bcis
(R5 =H) was also synthesized similarly (31% yield, two steps).
Next, vanadium(V) complex 2acis was treated with 2-amino-6-
tert-butylphenol and Ti(OiPr)4 in the ethanol/toluene under
reflux to give heterobimetallic complex 1acis (R5 =tBu, R6 =tBu)
in 49% yield. In the MALDI-TOF MS (negative mode) of 1acis,
the main mass was found at 1059.19, which corresponds to
the V-O-Ti linked heterodinuclear complex ([1acis–H]À, with Xl =
Xn =O, Xm =OH, see the Supporting Information).[14] The
1H NMR spectrum of 1acis showed the absence of alkoxide,
whereas the IR spectrum of 1acis supported the presence of
hydroxide. Furthermore, other substituted heterobimetallic
complexes 1bcis (R5 =tBu, R6 =SiMe3), 1ccis (R5 =tBu, R6 =H),
and 1dcis (R5 =H, R6 =H) were also synthesized. The formation
of these complexes was determined by MALDI-TOF MS (nega-
tive mode) analysis (see the Supporting Information).[15]
ylpropanal (8a) and benzaldehyde (9a) as the substrates. The
results of catalytic intermolecular cross-pinacol coupling reac-
tion are shown in Table 1. First, the conditions with the hetero-
dinuclear complex 1acis were used to give the desired 1,2-diol
10a as a minor product (17% yield; Table 1, entry 1).[16] Similar-
ly, the same reaction with Me3Si-substituted complex 1bcis led
to the heterocoupling product in 15% yield (Table 1, entry 2).
By switching the substituent on the titanium side of the het-
erodinuclear catalyst from tBu to H, the selectivity for the
cross-coupling dramatically increased, providing 1,2-diol 10a
in 69% yield (Table 1, entry 3). In the case of dinuclear catalyst
1dcis, the desired cross-coupling product was obtained in 73%
yield (syn/anti=59:41), and the molar ratio of 10a/11 a/12a
was enhanced to 7.1:1:1.1 (Table 1, entry 4). On the other hand,
the diastereoselectivity of the cross-coupling reaction was not
controlled. For comparison, the same reaction performed with
a mixture of mononuclear vanadium complex 13[17] and mono-
nuclear titanium complex 14[18] decreased the cross-selectivity
of 10a (10a/11 a/12a=2.4:1:0.1; Table 1, entry 5). In the ab-
sence of the vanadium and titanium catalysts, no cross-cou-
pling product was obtained (Table 1, entry 6).
With such complexes in hand, the intermolecular cross-pina-
col coupling reaction between aliphatic and aromatic alde-
hydes was examined (Table 1). The heterodinuclear catalyst 1cis
(5 mol%) was first activated to a low-valent species by using
Me3SiCl and an excess amount of activated Zn powder at
room temperature. Two equivalents of aliphatic aldehyde 8
were added to the reaction mixture, then aromatic aldehyde 9
was added dropwise over one hour. We initially chose 3-phen-
The increase of cross-selectivity may be accounted for as fol-
lows. The titanium-centered active site of the heterodinuclear
catalyst first activates aliphatic aldehyde 8a due to its higher
activity. Next, slowly added aromatic aldehyde 9a is activated
with the vacant vanadium center, then the thus-produced two
radical species of 8a and 9a would form the corresponding
Chem. Eur. J. 2014, 20, 1615 – 1621
www.chemeurj.org
1617
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
CÀC bond to give 1,2-diol 10a. On this occasion, a bulky tri-
methylsilyl- or tert-butyl group on the titanium side would in-
terrupt the reaction with aliphatic aldehyde 8a. Therefore, the
conditions with dinuclear catalyst 1dcis are considered to
afford the cross-coupling product preferentially. Thus, the in-
volvement of the heterodinuclear catalyst was suggested to be
essential for the reaction to work efficiently.
to be effective for cross-selectivity in the coupling reaction.
Such three-dimensionally arranged heterodinuclear complexes
will be applied to other reactions that require dual activation
by metals.
Experimental Section
Under the above optimized conditions using 1dcis, we next
investigated the cross-coupling reaction of a variety of aliphat-
ic aldehydes 8 and aromatic aldehydes 9. The results are sum-
marized in Table 2. The reaction between 3-phenylpropanal
General remarks:
1H, 13C, and 51 V NMR spectra were measured with a JEOL ECS-400
spectrometer; CDCl3 was used as a solvent and the residual solvent
peak (1H, d=7.26 ppm; 13C, d=77.16 ppm) was used as a reference.
51 V NMR spectra were referenced to VOCl3 (d=0 ppm) as an exter-
nal reference. Infrared spectra were recorded with a JASCO FT/IR-
480plus. Mass spectra were measured with a JEOL JMS-DX-303
spectrometer using fast atom bombardment (FAB) mode or with
a Bruker autoflex III mass spectrometer using matrix-assisted laser
desorption ionization time-of-flight (MALDI-TOF) mode and elec-
tron impact (EI) mode. Column chromatography was conducted on
silica-gel (Wakogel C-200). VO(OiPr)3 and Ti(OiPr)4 were distilled
under argon before use. Ethanol was distilled under argon over an
appropriate drying agent before use. Other reagents and solvents
were purchased from commercial sources.
Table 2. Cross-pinacol coupling reaction by using heterodinuclear cata-
[a,b]
lyst 1dcis
.
Monohemisalen vanadium complexes 2acis:
2-Amino-6-(tert-butyl)phenol (182 mg, 1.10 mmol) was added at RT
under argon to
a solution of disalicylaldehyde 3cis (458 mg,
0.736 mmol) in toluene (140 mL). The reaction mixture was stirred
at 908C for 1 h, then cooled to RT, dried over MgSO4, and evapo-
rated. The residue was purified by silica-gel column chromatogra-
phy (hexane/dichloromethane=1:0 to 1:3) to give the monoimine
compound (231 mg, 0.300 mmol, 41%). To a solution of the thus-
obtained monoimine compound (74.8 mg, 0.0972 mmol) in di-
chloromethane/ethanol (2.5 mL/0.5 mL, respectively) was added
VO(OiPr)3 (27.6 mL, 0.117 mmol) at RT under argon. The reaction
mixture was stirred for 2 h, then dichloromethane and ethanol
were removed by distillation under vacuum until a precipitation
appeared. The reaction mixture was then filtered through a mem-
brane filter and the residue was washed with hexane to give the
product 2acis (83.7 mg, 0.0951 mmol, 98%). 1H NMR (400 MHz,
CDCl3/CD3OD=20:1): d=9.49 (s, 0.36H), 9.45 (s, 0.64H), 8.86 (s,
0.36H), 9.85 (s, 0.64H), 6.50–7.40 (m, 29H), 3.69 (q, J=7.2 Hz, 2H),
1.47 (s, 9H), 1.22 ppm (t, J=7.2 Hz, 3H); 51V NMR (105.1 MHz,
CDCl3/CD3OD=20:1): d=À520, À526 ppm; IR (KBr): n˜ =3052,
3025, 2956, 2928, 2909, 2861, 1655, 1607, 1437, 1297, 1254, 996,
752, 698, 668 cmÀ1; HRMS (FAB): calcd. for C54H41NO5V: 834.2424
[MÀOEt]+; found: 834.2430.
Entry
Product
Yield [%][c,d]
Molar ratio
10 (syn/anti)
11
12
10
11
12
1
2
3
4
5
10a
10b
10c
10d
10e
73 (59:41)
81 (51:49)
70 (46:54)
88 (62:38)
69 (64:36)
10
19
7
36
5
23
14
17
11
24
7.1
4.2
9.5
2.4
13.2
1
1
1
1
1
1.1
0.3
1.1
0.2
2.3
[a] Reaction conditions (see the experimental section): 8 (0.4 mmol), 9
(0.2 mmol), 1dcis (0.01 mmol). [b] Slow addition (1 h) of 9 by using a sy-
ringe pump. [c] Yield of 10=(mole of 10)/0.2 mmolꢁ100, yield of 11 =
[(mole of 11)ꢁ2]/0.4 mmolꢁ100, yield of 12=[(mole of 12)ꢁ2]/
0.2 mmolꢁ100. [d] Determined by 1H NMR spectroscopic analysis of the
crude mixture.
and o-fluoro-substituted benzaldehyde showed a good yield
(81%; Table 2, entry 2). The reaction with 2-(trifluoromethyl)-
benzaldehyde gave 1,2-diol 10c in 70% yield (Table 2, entry 3).
When 2-phenylacetaldehyde was employed as an aliphatic al-
dehyde, cross-coupling product 10d was obtained in a high
yield (88%; Table 2, entry 4).[19a] The use of pentanal led to the
formation of 10e in 69% yield (Table 2, entry 5).[19b,c]
Monohemisalen vanadium complexes 2bcis:
To toluene (240 mL) were added 3cis (800 mg, 1.28 mmol) and 2-
aminophenol (209 mg, 1.92 mmol) at RT under argon. The reaction
mixture was stirred at 908C for 1 h, then cooled to RT, dried over
MgSO4, and evaporated. The residue was purified by silica-gel
column chromatography (hexane/dichloromethane=1:0 to 0:1) to
give a mixture of monoimine compound and 3cis (750.7 mg). The
mixture (750.7 mg) was dissolved in dichloromethane (56 mL) and
ethanol (5 mL), and VO(OiPr)3 (293 mL, 1.24 mmol) was added at RT
under argon. The reaction mixture was stirred for 2 h, then brine
was added and the aqueous layer was extracted twice with di-
chloromethane. The combined organic layer was dried over
MgSO4, and evaporated. The residue was purified by silica-gel
Conclusion
The dihemisalen ligand on a hexaarylbenzene scaffold was de-
signed, and heterodinuclear complexes 1cis with vanadium(V)
and titanium(IV) were synthesized from the key intermediate
3cis for the cross-pinacol coupling reaction. By using this novel
heterodinuclear catalysts, we have demonstrated the intermo-
lecular cross-pinacol coupling reaction between aliphatic and
aromatic aldehydes. The heterodinuclear catalyst was shown
Chem. Eur. J. 2014, 20, 1615 – 1621
www.chemeurj.org
1618
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
column chromatography (dichloromethane/ethanol=1:0 to 1:1) to
give the product 2bcis (326 mg, 0.396 mmol, 31%). 1H NMR
(400 MHz, CDCl3/CD3OD=20:1): d=9.44 (s, 0.31H), 9.41 (s, 0.69H),
8.83 (s, 0.69H), 8.81 (s, 0.31H), 6.50–7.60 (m, 29H), 3.61 (q, J=
7.2 Hz, 2H), 1.16 ppm (t, J=7.2 Hz, 3H); 51 V NMR (105.1 MHz,
CDCl3/CD3OD=20:1): d=À521, À527 ppm; IR (KBr): n˜ =3052,
3025, 2960, 2933, 2853, 1654, 1607, 1557, 1439, 1301, 751, 699,
545 cmÀ1; HRMS (FAB): calcd. for C50H33NO5V: 778.1798 [MÀOEt]+;
found: 778.1790.
Heterodihemisalen complex 1bcis:
Ti(OiPr)4 (53.3 mL, 0.182 mmol) was added at RT under argon to
a solution of 2acis (80.0 mg, 0.0909 mmol) and 2-amino-6-(trimeth-
ylsilyl)phenol (16.5 mg, 0.0909 mmol) in toluene/ethanol (6 mL/
3 mL, respectively). The reaction mixture was stirred at 908C for
2 h, then cooled to RT and purified by silica-gel column chroma-
tography (hexane/ethyl acetate=1:0 to 1:1) to give the product
1bcis (30.3 mg, 0.0281 mmol, 31%). MS (MALDI): calcd. for
C63H52N2O7SiTiV: 1075.25 [MÀH]À; found: 1074.81.
Heterodihemisalen complex 1acis:
Heterodihemisalen complex 1ccis:
Ti(OiPr)4 (40.0 mL, 0.136 mmol) was added to a solution of 2acis
(60.0 mg, 0.0682 mmol) and 2-amino-6-(tert-butyl)phenol (11.3 mg,
0.0682 mmol) in toluene/ethanol (4 mL/2 mL, respectively) at RT
under argon. The reaction mixture was stirred at 908C for 2 h, then
cooled to RT, and evaporated. The mixture was purified by silica-
gel column chromatography (hexane/ethyl acetate=1:0 to 1:2) to
give the product 1acis (35.1 mg, 0.0331 mmol, 49%). 1H NMR
(400 MHz, CDCl3): d=8.86 (s, 1H), 8.31 (s, 1H), 6.70–7.30 (m, 30H),
6.60 (dd, J=8.0, 8.0 Hz, 1H), 6.42 (dd, J=7.2, 7.2 Hz, 1H), 1.48 (s,
9H), 1.16 ppm (s, 9H); 13C NMR (100 MHz, CDCl3): d=163.99,
163.24, 161.16, 161.04, 155.28, 153.96, 141.55, 140.97, 140.87,
140.70, 140.64, 140.58, 140.34, 139.26, 139.10, 138.45, 138.13,
137.53, 137.01, 136.39, 132.51, 132.38, 132.27, 131.87, 131.67,
131.55, 131.46, 130.68, 129.75, 128.85, 127.35, 126.88, 126.69,
126.64, 126.60, 126.44, 126.15, 125.69, 125.51, 125.35, 122.61,
120.37, 119.71, 119.66, 119.51, 118.18, 112.41, 112.24, 34.79, 34.71,
29.55, 29.21, 22.90, 18.63 ppm; 51 V NMR (105.1 MHz, CDCl3): d=
À573 ppm; IR (KBr): n˜ =3626, 3054, 2953, 2907, 2865, 1607, 1435,
Ti(OiPr)4 (80 mL, 0.272 mmol) at RT under argon was added to a so-
lution of 2acis (120 mg, 0.136 mmol) and 2-aminophenol (14.9 mg,
0.136 mmol) in toluene/ethanol (20 mL/2 mL, respectively). The re-
action mixture was stirred at 908C for 2 h, then cooled to RT and
purified by silica-gel column chromatography (dichloromethane/
ethanol=1:0 to 4:1) to give the product 1ccis (50.6 mg,
0.0457 mmol, 37%). In the MALDI-TOF MS (negative mode) of 1ccis,
the dehydrated dimer species [2(1ccis)ÀH2O] was also observed,
see the Supporting Information for details. MS (MALDI): calcd. for
C60H44N2O7TiV: 1003.21 [MÀH]À; found: 1003.07; calcd. for
C
120H88N4O13Ti2V2: 1990.42 [2MÀH2O]À; found: 1990.34.
Heterodihemisalen complex 1dcis:
Ti(OiPr)4 (85.6 mL, 0.292 mmol) was added at RT under argon to
a solution of 2bcis (120 mg, 0.146 mmol) and 2-aminophenol
(15.9 mg, 0.146 mmol) in toluene/ethanol (20 mL/2 mL, respective-
ly). The reaction mixture was stirred at 908C for 2 h, then cooled to
RT and purified by silica-gel column chromatography (dichloro-
methane/ethanol=1:0 to 4:1) to give the product 1dcis (61.0 mg,
0.0643 mmol, 44%). In the MALDI-TOF MS (negative mode) of
1dcis, the dehydrated dimer species [21dcisÀH2O] was also ob-
served, see the Supporting Information for details. MS (MALDI):
calcd. for C56H36N2O7TiV: 947.14 [MÀH]À; found: 946.99; calcd. for
C112H72N4O13Ti2V2: 1878.29 [2MÀH2O]À; found: 1878.12.
1372, 1255, 752 cmÀ1
; HRMS (FAB): calcd. for C64H52N2O6TiV:
1043.2744 [MÀOH]+; found: 1043.2752; MS (MALDI): calcd. for
C64H52N2O7TiV: 1059.27 [MÀH]À; found: 1059.19.
2-Amino-6-(trimethylsilyl)phenol:
2-Bromo-6-nitrophenol (1.0 g, 4.59 mmol) was added at RT under
argon to HN(SiMe3)2 (3.0 mL, 14.1 mmol), and the mixture was
heated to reflux and stirred for 2 h. HN(SiMe3)2 was removed from
the reaction mixture by distillation under vacuum. THF (15 mL) and
a solution of PhLi (1.13m in Et2O, 8.1 mL, 9.17 mmol) were added
at À848C and the reaction mixture was stirred for 1 h. The ice
chloroform bath was then removed and the mixture was stirred for
1 h at RT. Saturated aqueous NH4Cl was added and the aqueous
layer was extracted twice with ether. The combined organic layer
was washed with brine, dried over MgSO4, and evaporated. The
residue was purified by silica-gel column chromatography (hexane/
General procedure for the intermolecular cross-pinacol cou-
pling reaction:
Me3SiCl (103 mL 0.80 mmol) was added at RT under argon to a solu-
tion of 1dcis (9.5 mg, 0.010 mmol) and activated Zn dust (129 mg,
2.0 mmol) in THF (2 mL). The reaction mixture was stirred for
10 min, then aliphatic aldehyde 8 (0.40 mmol) was added. A solu-
tion of aromatic aldehyde 9 (0.05m in THF, 4 mL, 0.20 mmol) was
added dropwise over 1 h to the mixture, which was then stirred
for 10 min at RT. 1m HCl was added and the aqueous layer was ex-
tracted twice with ethyl acetate. The combined organic layer was
washed with 6m HCl, saturated aqueous NaHCO3, and brine, dried
over MgSO4, and evaporated. The yields were determined by
1H NMR spectroscopic analysis with 1,3,5-trimethoxybenzene
(11.2 mg, 0.0667 mmol) as an internal standard. The assignment of
the syn/anti isomers of 1,2-diol 10 was determined by 2D NOESY
experiments with 10anti after the formation of the acetonide 15 as
described below.
dichloromethane=1:0
to
5:1)
to
give
2-nitro-6-(tri-
methylsilyl)phenol as
a mixture with trimethyl(phenyl)silane
[139.2 mg, 2-nitro-6-(trimethylsilyl)phenol/trimethyl(phenyl)silane=
73:27]. Ethanol (15 mL) and 10 wt% Pd on charcoal (33.1 mg,
0.0310 mmol) were added to the mixture, which was then hydro-
genated with H2 for 3 h at RT. The reaction mixture was filtered,
evaporated, and the residue was purified by silica-gel column chro-
matography (hexane/ethyl acetate=1:0 to 2:1) to give 2-amino-6-
(trimethylsilyl)phenol (57.9 mg, 0.319 mmol, 7%). 1H NMR
(400 MHz, CDCl3): d=6.92 (dd, J=7.6, 1.6 Hz, 1H), 6.87 (dd, J=7.6,
1.6 Hz, 1H), 6.81 (dd, J=7.6, 7.6 Hz, 1H), 0.32 ppm (s, 9H); 13C NMR
(100 MHz, CDCl3): d=151.32, 132.79, 127.26, 125.89, 121.21, 120.92,
À0.61 ppm; IR (KBr): n˜ =3387, 3299, 3065, 2953, 2698, 2638, 1591,
1449, 1406, 1368, 1293, 1249, 1219, 1205, 1157, 1112, 915, 897, 838,
787, 757, 693, 642, 605 cmÀ1; HRMS (FAB): calcd. for C9H15NOSi:
181.0923 [M+]; found: 181.0922.
1,4-Diphenylbutane-1,2-diol (10a):
According to the general procedure for the intermolecular cross-pi-
nacol coupling reaction, 3-phenylpropanal (8a) and benzaldehyde
(9a) were reductively coupled to give 10a (73%).
Chem. Eur. J. 2014, 20, 1615 – 1621
www.chemeurj.org
1619
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Compound 10asyn
:
Compound 10canti:
1H NMR (400 MHz, CDCl3): d=7.20–7.40 (m, 7H), 7.10–7.20 (m, 3H),
4.51 (br, 1H), 3.75 (br, 1H), 2.82 (m, 1H), 2.61 (m, 1H), 1.70 (m, 1H),
1.59 ppm (m, 1H).
1H NMR (400 MHz, CDCl3): d=7.88 (d, J=7.6 Hz, 1H), 7.65 (d, J=
7.6 Hz, 1H), 7.58 (dd, J=7.6, 7.6 Hz, 1H), 7.41 (dd, J=7.6, 7.6 Hz,
1H), 7.26 (dd, J=7.2, 7.2 Hz, 2H), 7.17 (t, J=7.2 Hz, 1H), 7.15 (d,
J=7.2 Hz, 2H), 5.14 (s, 1H), 3.96 (m, 1H), 2.86 (m, 1H), 2.60 (m,
1H), 2.41 (d, J=3.2 Hz, 1H), 1.95 (d, J=5.6 Hz, 1H), 1.80 (m, 1H),
1.74 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=141.97, 139.54,
132.26, 129.09, 128.55, 128.52, 128.15 (q, J=29.6 Hz), 128.06,
126.01, 125.91 (q, J=5.7 Hz), 124.46 (q, J=272.7 Hz), 74.18, 72.34,
Compound 10aanti
:
1H NMR (400 MHz, CDCl3): d=7.20–7.40 (m, 7H), 7.10–7.20 (m, 3H),
4.69 (dd, J=3.2, 3.2 Hz, 1H), 3.86 (m, 1H), 2.83 (m, 1H), 2.64 (m,
1H), 2.28 (d, J=3.2 Hz, 1H), 1.87 (d, J=5.2 Hz, 1H), 1.77 (m, 1H),
1.61 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=142.02, 140.38,
128.60ꢁ2, 128.51, 128.12, 126.94, 125.98, 77.27, 74.57, 33.48,
32.22 ppm; IR (KBr): n˜ =3343, 3251, 2934, 1452, 699 cmÀ1; HRMS
(FAB): calcd for C16H17O2: 241.1234 [MÀH]À; found: 241.1232.
32.82, 32.21 ppm; IR (KBr): n˜ =3323, 2957, 1312, 1162, 1117 cmÀ1
;
HRMS (FAB): calcd for C17H16F3O2: 309.1108 [MÀH]À; found:
309.1101.
General procedure for the formation of the acetonide 15 of
1,2-diol 10anti
:
Compound 10anti, 10-camphorsulfonic acid (10 mol%), MS3A (23 g),
and 2,2-dimethoxypropane (300 mol%) were added to dichlorome-
thane (15 mL) at RT under argon. The reaction mixture was stirred
for 1 h, then saturated aqueous NaHCO3 was added. MS3A was re-
moved from the reaction mixture by filtration and the aqueous
layer was extracted twice with dichloromethane. The combined or-
ganic layer was washed with brine, dried over MgSO4, and evapo-
rated. The residue was purified by silica-gel column chromatogra-
phy (hexane/ethyl acetate=1:0 to 8:1) to give 15.
1-(2-Fluorophenyl)-4-phenylbutane-1,2-diol (10b):
According to general procedure for the intermolecular cross-pina-
col coupling reaction, 3-phenylpropanal (8a) and 2-fluorobenzalde-
hyde were reductively coupled to give 10b (81%).
Compound 10bsyn
:
1H NMR (400 MHz, CDCl3): d=7.42 (dd, J=7.6, 7.6 Hz, 1H), 7.20–
7.30 (m, 3H), 7.10–7.20 (m, 4H), 7.03 (m, 1H), 4.87 (dd, J=4.8,
4.8 Hz, 1H), 3.79 (m, 1H), 2.81 (m, 1H), 2.64 (m, 1H), 2.57 (d, J=
4.8 Hz, 1H), 2.33 (d, J=4.8 Hz, 1H), 1.60–1.80 ppm (m, 2H).
2,2-Dimethyl-4-phenethyl-5-phenyl-1,3-dioxolane (15a):
According to the general procedure for the formation of the aceto-
nide 15 of 1,2-diol, 10aanti (77.2 mg, 0.319 mmol) was converted
into 15a (64.5 mg, 0.228 mmol, 71%). 1H NMR (400 MHz, CDCl3):
d=7.20–7.40 (m, 7H), 7.14 (dd, J=7.2, 7.2 Hz, 1H), 7.02 (d, J=
7.2 Hz, 2H), 5.19 (d, J=6.8 Hz, 1H), 4.35 (m, 1H), 2.64 (m, 1H), 2.44
(m, 1H), 1.66 (s, 3H), 1.46 (s, 3H), 1.45 (m, 1H), 1.23 ppm (m, 1H);
13C NMR (100 MHz, CDCl3): d=141.92, 137.97, 128.61, 128.41,
128.34, 127.90, 127.09, 125.90, 108.35, 80.10, 78.26, 33.53, 32.43,
Compound 10banti
:
1H NMR (400 MHz, CDCl3): d=7.53 (ddd, J=7.6, 7.6, 2.0 Hz, 1H),
7.20–7.30 (m, 3H), 7.10–7.20 (m, 4H), 7.02 (ddd, J=9.2, 7.6, 1.2 Hz,
1H), 5.09 (dd, J=4.4, 4.4 Hz, 1H), 3.97 (m, 1H), 2.81 (m, 1H), 2.64
(m, 1H), 2.38 (d, J=4.4 Hz, 1H), 1.92 (d, J=5.6 Hz, 1H), 1.74 (m,
1H), 1.58 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=160.03 (d,
J=244.1 Hz), 141.92, 129.40 (d, J=8.6 Hz), 128.58, 128.55 (d, J=
5.7 Hz), 128.52, 127.30 (d, J=13.3 Hz), 126.02, 124.44 (d, J=2.9 Hz),
115.34 (d, J=21.9 Hz), 73.79, 70.91, 33.06, 32.20 ppm; IR (KBr): n˜ =
3369, 3253, 2936, 1454, 1101, 1064 cmÀ1; HRMS (FAB): calcd for
C16H16FO2: 259.1140 [MÀH]À; found: 259.1135.
27.79, 25.36 ppm; IR (KBr): n˜ =3066, 3031, 1700, 1288, 702 cmÀ1
;
HRMS (EI): calcd for C19H23O2: 283.1693 [M+H]+; found: 283.1696.
4-(2-Fluorophenyl)-2,2-dimethyl-5-phenethyl-1,3-dioxolane
(15b):
According to the general procedure for the formation of the aceto-
nide 15 of 1,2-diol, 10banti (16.3 mg, 0.0626 mmol) was converted
1
4-Phenyl-1-(2-(trifluoromethyl)phenyl)butane-1,2-diol (10c):
into 15b (10.2 mg, 0.0340 mmol, 54%). H NMR (400 MHz, CDCl3):
d=7.52 (dd, J=7.2, 7.2 Hz, 1H), 7.20–7.30 (m, 3H), 7.10–7.20 (m,
2H), 7.04 (d, J=7.2 Hz, 2H), 7.00 (m, 1H), 5.50 (d, J=6.8 Hz, 1H),
4.46 (m, 1H), 2.68 (m, 1H), 2.49 (m, 1H), 1.66 (s, 3H), 1.49 (s, 3H),
1.42 (m, 1H), 1.31 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=
159.86 (d, J=244.0 Hz), 141.92, 129.18 (d, J=7.6 Hz), 128.58,
128.29, 128.28 (d, J=3.8 Hz), 125.90, 125.44 (d, J=13.4 Hz), 124.23
(d, J=2.9 Hz), 114.97 (d, J=21.0 Hz), 108.33, 77.58, 73.94 (d, J=
3.8 Hz), 33.39, 32.37, 27.81, 25.38 ppm; IR (KBr): n˜ =2958, 2930,
1728, 1261, 1057 cmÀ1; HRMS (EI): calcd for C19H22FO2: 301.1598
[M+H]+; found: 301.1607.
According to general procedure for the intermolecular cross-pina-
col coupling reaction, 3-phenylpropanal (8a) and 2-(trifluorometh-
yl)-benzaldehyde were reductively coupled to give 10c (70%).
Compound 10csyn
:
1H NMR (400 MHz, CDCl3): d=7.65 (d, J=7.6 Hz, 1H), 7.62 (d, J=
7.6 Hz, 1H), 7.56 (dd, J=7.6, 7.6 Hz, 1H), 7.40 (dd, J=7.6, 7.6 Hz,
1H), 7.25 (dd, J=7.2, 7.2 Hz, 2H), 7.16 (t, J=7.2 Hz, 1H), 7.11 (d, J=
7.2 Hz, 2H), 4.96 (dd, J=4.4, 4.4 Hz, 1H), 3.78 (m, 1H), 2.84 (m, 1H),
2.69 (d, J=4.4 Hz, 1H), 2.63 (m, 1H), 2.37 (d, J=4.4 Hz, 1H), 1.84
(m, 1H), 1.60 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=141.63,
140.32, 132.33, 128.49ꢁ2, 128.44, 128.10, 127.93 (q, J=29.5 Hz),
126.02, 125.91 (q, J=5.7 Hz), 124.38 (q, J=272.7 Hz), 74.86, 72.39,
2,2-Dimethyl-4-phenethyl-5-(2-(trifluoromethyl)phenyl)-1,3-
dioxolane (15c):
According to the general procedure for the formation of the aceto-
nide 15 of 1,2-diol, 10canti (21.7 mg, 0.070 mmol) was converted
into 15c (4.4 mg, 0.0126 mmol, 18%). 1H NMR (400 MHz, CDCl3):
d=7.78 (d, J=7.6 Hz, 1H), 7.62 (d, J=7.6 Hz, 1H), 7.55 (dd, J=7.6,
34.58, 32.11 ppm; IR (KBr): n˜ =3245, 2949, 1310, 1167, 1121 cmÀ1
;
HRMS (FAB): calcd for C17H16F3O2: 309.1108 [MÀH]À; found:
309.1105.
Chem. Eur. J. 2014, 20, 1615 – 1621
www.chemeurj.org
1620
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Int. Ed. 2001, 40, 1116–1119; k) S. Fischer, U. Groth, M. Jung, M. Linden-
maier, T. Vogel, Tetrahedron Lett. 2005, 46, 6679–6682; l) U. Groth, M.
Jung, T. Vogel, Chem. Eur. J. 2005, 11, 3127–3135; m) V. Nair, S. Ros,
C. N. Jayan, N. P. Rath, Tetrahedron Lett. 2002, 43, 8967–8969; n) Y.-S.
Yang, Z.-L. Shen, T.-P. Loh, Org. Lett. 2009, 11, 2213–2215.
7.6 Hz, 1H), 7.38 (dd, J=7.6, 7.6 Hz, 1H), 7.21 (dd, J=7.2, 7.2 Hz,
2H), 7.13 (t, J=7.2 Hz, 1H), 7.02 (d, J=7.2 Hz, 2H), 5.57 (s, 1H),
4.41 (m, 1H), 2.72 (m, 1H), 2.44 (m, 1H), 1.68 (s, 3H), 1.49 (s, 3H),
1.34 (m, 1H), 1.12 ppm (m, 1H); 13C NMR (100 MHz, CDCl3): d=
141.81, 136.57, 131.93, 128.93, 128.52, 128.41, 127.89, 127.54 (q, J=
30.5 Hz), 125.92, 125.76 (q, J=5.7 Hz), 124.38 (q, J=272.7 Hz),
108.37, 78.42, 75.67, 33.82, 32.71, 27.63, 25.05 ppm; IR (KBr): n˜ =
2931, 1314, 1162, 1123 cmÀ1; HRMS (EI): calcd for C20H22F3O2:
351.1566 [M+H]+; found: 351.1569.
[6] T. Amaya, A. Miyasaka, T. Hirao, Tetrahedron Lett. 2011, 52, 4567–4569.
[7] a) J. Sun, Z. Dai, C. Li, X. Pan, C. Zhu, J. Organomet. Chem. 2009, 694,
3219–3221; b) We obtained the experimental results as follows. The
mononuclear hemisalen-VV complex activated an aromatic aldehyde in
the presence of Me3SiCl and Zn to undergo the pinacol coupling but
did not activate aliphatic aldehydes under similar conditions (see
Table S1 in the Supporting Information); c) M. Bandini, P. G. Cozzi, S.
Morganti, A. Umani-Ronchi, Tetrahedron Lett. 1999, 40, 1997–2000;
d) M. S. Dunlap, K. M. Nicholas, Synth. Commun. 1999, 29, 1097–1106;
e) A. Bensari, J.-L. Renaud, O. Riant, Org. Lett. 2001, 3, 3863–3865.
[8] A. Miyasaka, T. Amaya, T. Hirao, Tetrahedron Lett. 2012, 53, 5589–5592.
[9] For examples of the step-by-step synthesis of heterodinuclear salen
complexes, see: a) A. M. Castilla, S. Curreli, E. C. Escudero-Adꢂn, M. M.
Belmonte, J. Benet-Buchholz, A. W. Kleij, Org. Lett. 2009, 11, 5218–5221;
b) H. Houjou, M. Ito, K. Araki, Inorg. Chem. 2009, 48, 10703–10707.
[10] M. A. Ogliaruso, M. G. Romanelli, E. I. Becker, Chem. Rev. 1965, 65, 261–
367.
[11] R. C. Larock, L. W. Harrison, J. Am. Chem. Soc. 1984, 106, 4218–4227.
[12] Synthesis of the desymmetrized monomethoxy compounds 7cis and
7trans are described in the Supporting Information, Scheme S1.
[13] Synthesis and characteristic of mononuclear vanadium(V) hemisalen
complexes on a hexaarylbenzene scaffold are described in Ref. 8.
[14] The coordination geometry is not clear at this stage. We have already
reported V-O-V linked divanadium(V) complexes on the same ligands.[8]
TiIV-O-VV linked hetero complex and/or TiIV-OH complexes are described,
see: a) R. Z. Khaliullin, A. T. Bell, J. Phys. Chem. B 2002, 106, 7832–7838;
b) F. Caruso, L. Massa, A. Gindulyte, C. Pettinari, F. Marchetti, R. Pettinari,
M. Ricciutelli, J. Costamagna, J. C. Canales, J. Tanski, M. Rossi, Eur. J.
Inorg. Chem. 2003, 3221–3232.
Acknowledgements
A. M. expresses his special thanks for The Global COE (center
of excellence) Program Global Education and Research Center
for Bio-Environmental Chemistry and Grants for Excellent Grad-
uate Schools of Osaka University. This work was partially sup-
ported by a Grant-in-Aid for Challenging Exploratory Research
(24655079) from the Japan Society for the Promotion of Sci-
ence (JSPS). Financial support from JST, ACT-C is also acknowl-
edged. Thanks are due to the donation of VO(OiPr)3 from the
Nichia corporation.
Keywords: CÀC coupling · heterometallic complexes · ligand
design · redox chemistry · titanium · vanadium
[1] For a review, see: A. Chatterjee, N. N. Joshi, Tetrahedron 2006, 62,
12137–12158.
[2] K. C. Nicolaou, Z. Yang, J. J. Liu, H. Ueno, P. G. Nantermet, R. K. Guy, C. F.
Claiborne, J. Renaud, E. A. Couladouros, K. Paulvannan, E. J. Sorensen,
Nature 1994, 367, 630–634.
[15] In the MALDI-TOF MS (negative mode) of the heterodinuclear com-
plexes without a bulky substituent on the titanium side such as 1ccis
and 1dcis, the corresponding dimer species were also observed, see the
Supporting Information for details.
[3] B. Kammermeier, G. Beck, D. Jacobi, H. Jendralla, Angew. Chem. 1994,
106, 719–721; Angew. Chem. Int. Ed. Engl. 1994, 33, 685–687.
[4] a) T. Hirao, T. Hasegawa, Y. Muguruma, I. Ikeda, J. Org. Chem. 1996, 61,
366–367; For a review, see: b) T. Hirao, Chem. Rev. 1997, 97, 2707–
2724; c) T. Hirao, M. Asahara, Y. Muguruma, A. Ogawa, J. Org. Chem.
1998, 63, 2812–2813; d) T. Hirao, B. Hatano, M. Asahara, Y. Muguruma,
A. Ogawa, Tetrahedron Lett. 1998, 39, 5247–5248; e) B. Hatano, A.
Ogawa, T. Hirao, J. Org. Chem. 1998, 63, 9421–9424; f) T. Hirao, B.
Hatano, Y. Imamoto, A. Ogawa, J. Org. Chem. 1999, 64, 7665–7667; g) T.
Hirao, A. Ogawa, M. Asahara, Y. Muguruma, H. Sakurai, Org. Synth. 2005,
81, 26–32; h) X. Xu, T. Hirao, J. Org. Chem. 2005, 70, 8594–8596.
[5] For a review, see: a) B. S. Terra, F. Macedo Jr., ARKIVOC 2012, i, 134–151;
b) J. H. Freudenberger, A. W. Konradi, S. F. Pedersen, J. Am. Chem. Soc.
1989, 111, 8014–8016; c) P. M. Takahara, J. H. Freudenberger, A. W. Kon-
radi, S. F. Pedersen, Tetrahedron Lett. 1989, 30, 7177–7180; d) A. W. Kon-
radi, S. J. Kemp, S. F. Pedersen, J. Am. Chem. Soc. 1994, 116, 1316–1323;
e) J. Park, S. F. Pedersen, J. Org. Chem. 1990, 55, 5924–5926; f) M. Kang,
J. Park, S. F. Pedersen, Synlett 1997, 41–43; g) R. Annunziata, M. Cinqui-
ni, F. Cozzi, P. Giaroni, Tetrahedron: Asymmetry 1990, 1, 355–358; h) N.
Taniguchi, M. Uemura, J. Am. Chem. Soc. 2000, 122, 8301–8302; i) M.
Shimizu, A. Iwata, H. Makino, Synlett 2002, 1538–1540; j) K. Takai, R.
Morita, C. Toratsu, Angew. Chem. 2001, 113, 1150–1153; Angew. Chem.
[16] Syn and anti conformations were determined on the basis of 2D-NOESY
experiments after the formation of the acetonide 15 from 10, see the
Supporting Information for details.
[17] For the preparation of mononuclear vanadium(V) hemisalen complex,
see: M. J. Clague, N. L. Keder, A. Butler, Inorg. Chem. 1993, 32, 4754–
4761.
[18] For the preparation of mononuclear titanium(IV) hemisalen complex,
see: D. Owiny, S. Parkin, F. T. Ladipo, J. Organomet. Chem. 2003, 678,
134–141.
[19] The chemical shifts of the 1H NMR spectra for the cross-coupling prod-
ucts 10d and 10e were identical with the reported spectra, see: a) T.
Kawakami, I. Shibata, A. Baba, J. Org. Chem. 1996, 61, 82–87; b) G. Bel-
lucci, C. Chiappe, A. Cordoni, Tetrahedron: Asymmetry 1996, 7, 197–
202; c) P. Jiao, M. Kawasaki, H. Yamamoto, Angew. Chem. 2009, 121,
3383–3386; Angew. Chem. Int. Ed. 2009, 48, 3333–3336.
Received: October 9, 2013
Published online on January 8, 2014
Chem. Eur. J. 2014, 20, 1615 – 1621
www.chemeurj.org
1621
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim