Indium-catalyzed reductive coupling of aromatic carbonyl compounds and imines in the presence of aluminum and chlorosilanes

Article abstract of DOI:10.1002/hc.1049

Reductive homocoupling of aromatic aldehydes, ketones, and imines has been achieved in tetrahydrofuran (THF) at room temperature using a catalytic amount of InCl₃ (0.5-3.0 mol %) under a nitrogen atmosphere in the presence of chlorotrimethylsilane (TMSCl) and aluminum metal (Al) to provide the corresponding 1,2-diols and 1,2-diamines, respectively, in good to moderate yields. Other indium compounds such as In(NO₃)₃, cyclopentadienylindium, and indium metal have also been revealed to be effective as catalysts. The catalytic effect of the indium compound is remarkable, and, thus, without it, no reaction occurs in the case of aromatic aldehydes and aldimines, and an induction period is quite long in the case of aromatic ketones. Without either TMSCl or Al, no reaction proceeds even in the presence of the catalyst. Unfortunately, the diastereoselectivity of the products (dl and meso) is not high. Although the precise reaction scheme is not yet clear, we tentatively propose that a redox-active In-Al alloy might be formed on the surface of aluminum in the presence of TMSCl, and an electron transfer from the alloy to substrate might occur.

Full text of DOI:10.1002/hc.1049

Heteroatom Chemistry
Volume 12, Number 4, 2001
Indium-Catalyzed Reductive Coupling of
Aromatic Carbonyl Compounds and Imines in
the Presence of Aluminum and Chlorosilanes
Seiji Ohtaka, Kenji Mori, and Sakae Uemura
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto
University, Sakyo-ku, Kyoto 606-8501, Japan
Received 4 January 2001; revised 16 February 2001
occur. ꢀ 2001 John Wiley & Sons, Inc. Heteroatom
ABSTRACT: Reductive homocoupling of aromatic
Chem 12:309–316, 2001
aldehydes, ketones, and imines has been achieved in
tetrahydrofuran (THF) at room temperature using a
catalytic amount of InCl3 (0.5–3.0 mol %) under a ni-
trogen atmosphere in the presence of chlorotrimethyl-
silane (TMSCl) and aluminum metal (Al) to provide
the corresponding 1,2-diols and 1,2-diamines, respec-
tively, in good to moderate yields. Other indium com-
pounds such as In(NO3)3, cyclopentadienylindium,
and indium metal have also been revealed to be effec-
tive as catalysts. The catalytic effect of the indium
compound is remarkable, and, thus, without it, no re-
action occurs in the case of aromatic aldehydes and
aldimines, and an induction period is quite long in the
case of aromatic ketones. Without either TMSCl or Al,
no reaction proceeds even in the presence of the cata-
lyst. Unfortunately, the diastereoselectivity of the prod-
ucts (dl and meso) is not high. Although the precise
reaction scheme is not yet clear, we tentatively propose
that a redox-active In-Al alloy might be formed on the
surface of aluminum in the presence of TMSCl, and
an electron transfer from the alloy to substrate might
INTRODUCTION
The organic chemistry of indium is of current inter-
est from the viewpoint of organic synthesis [1]. Thus,
indium and its compounds have worked as reagents
as well as catalysts in some carbon–carbon bond-
forming reactions, such as allylation of carbonyl
compounds [2], Reformatsky reactions [3], aldol re-
actions [4], Diels-Alder reactions [5], Michael reac-
tions [6], Friedel-Crafts reactions [7], and reductive
coupling reactions [8]. In the cases of catalytic re-
actions, however, a rather large amount of indium
salts (10–20 mol %) has normally been employed. We
have now disclosed a new and quite efficient cata-
lytic activity of indium(III) chloride (0.5–3.0 mol %)
in reductive homocoupling of carbonyl compounds
and imines. It has so far been reported that the use
of a stoichiometric amount of indium metal induced
the reductive homocoupling of aromatic aldehydes
[8a] and imines [8b] in water or water-alcohol mix-
ture. Our new system consists of the combination of
chlorotrimethylsilane (TMSCl), aluminum (Al), and
a catalytic amount of an indium compound for this
reductive coupling reaction. It is worth noting that
catalytic systems for the reductive coupling using a
catalytic amount of transition metal complex
(mainly Ti and V), and TMSCl with a co-reductant
Dedicated to Prof. Naoki Inamoto on the occasion of his 72nd
birthday.
Correspondence to: Sakae Uemura.
ꢀ 2001 John Wiley & Sons, Inc.
309

310 Ohtaka, Mori, and Uemura
TABLE 1 Effect of Reductant for Reductive Coupling of
Benzaldehyde (1a)a
metal such as Zn, Al, and Mg have recently been de-
veloped by several groups [9].
Time
Yield
Entry
Reductant (equiv)b
Al (4)
(h)c (%) of 2ad dl/mesoe
RESULTS AND DISCUSSION
24f
5f
8
2
2
2
2
2
2
4
2
5
5
0
0
—
—
Reductive Homocoupling of Aromatic Aldehydes
1
2g
3h
4h
5
Al (4)
Treatment of benzaldehyde (1a) with aluminum
metal (Al, 4 equiv), chlorotrimethylsilane (TMSCl, 4
equiv), and a catalytic amount of InCl3 (5 mol %) in
tetrahydrofuran (THF) under a nitrogen atmosphere
at room temperature for 2 hours afforded 1,2-di-
phenyl-1,2-ethanediol (2a) in 45% yield (dl/meso ꢂ
52/48) (Scheme 1). Without either Al or TMSCl, the
reaction did not occur even in the presence of InCl3.
On the other hand, without the addition of InCl3, no
reaction proceeded in the presence of both TMSCl
and Al [10] even under sonication. It was found that
the amount of InCl3 can be reduced to 0.5 mol % with
the yield of 2a being increased to 61%. The yield of
the expected diols was somewhat low despite a com-
plete conversion of 1a, and a small amount of benzyl
alcohol and small amounts of many unidentified
compounds were detected. It was also disclosed that
other several indium(III) and (I) compounds and in-
dium metal (powder) work as effective catalysts like
InCl3 (Table 1). We examined the effect of other met-
als such as Zn [11], Mg [12], and In [8] as a reduc-
tant. In the cases of Zn and Mg, the reaction pro-
ceeded to give 2a in moderate yield (up to 45%), but
no catalytic effect of InCl3 was observed in the cases
of Zn and In, as shown in Table 1. The diastereose-
lectivity was not affected much by changing the re-
action temperature in the range between reflux (58/
42) to 0ЊC (61/39), while the reaction did not proceed
at much lower temperature. Similarly, a great
change of selectivity was not observed when the re-
action was carried out in a variety of solvents, such
as dimethylformamide, 1,4-dioxane, acetonitrile,
and dichloromethane, as shown in Table 2, the prod-
uct yield being highest in the reaction using THF.
Many chlorosilanes, such as chlorotriisopropylsi-
lane, chlorodiphenylmethylsilane, chlorotriphenyl-
silane, dichlorodimethylsilane and bis(dimethyl-
lnCl3 (0.001) ꢁ Al (4)
lnCl3 (0.005) ꢁ Al (4)
lnCl3 (0.01) ꢁ Al (4)
lnCl3 (0.02) ꢁ Al (4)
lnCl3 (0.05) ꢁ Al (4)
lnCl3 (0.1) ꢁ Al (4)
ln (0.005) ꢁ Al (4)
39
61
56
52
45
18
54
34
59
54
57
43
42
0
59/41
57/43
55/45
54/46
52/48
55/45
53/47
59/41
56/44
57/43
57/43
52/48
59/41
—
6
7
8
9h
10g,h ln (0.005) ꢁ Al (4)
11h
12h
13h
14
lnCl (0.005) ꢁ Al (4)
lnCp (0.005) ꢁ Al (4)
ln(NO3)3 (0.005) ꢁ Al (4)
Zn (4)
Mg (4)
ln (4)
1
15
20
24i
4
16
17h
18h
lnCl3 (0.005) ꢁ Zn (4)
lnCl3 (0.005) ꢁ ln (4)
40
0
59/41
—
7
aReaction conditions: 1a (0.106 g, 1 mmol), TMSCI (0.5 mL, 4 mmol),
THF (10 mL), rt, N2.
bAl, foil; ln, powder; Zn, powder; Mg, ribbon.
cThe time for 100% conversion of 1a.
dIsolated yield. The formation of 0.5 mmol of 2a corresponds to 100%
yield.
eDetermined by 1H NMR.
fNo reaction.
gUnder sonication in a BRANSONIC ultrasonic cleaner bath, which
delivered a 47 kHz wave, with a fixed electrical power of 125 W.
hFive-fold scale reaction.
iThe conversion was not determined.
TABLE 2 Effect of Solvent for Reductive Coupling of Benz-
aldehyde (1a)a
Entry
Solvent
THF
Et2O
1,4-dioxane
DME
Time (h)b Yield (%) of 2ac dl/mesod
1
2
3
4
5
6
7
8
9
2
48e
24
18
6
45
18
21
14
33
21
18
0
52/48
24/76
48/52
45/55
60/40
49/51
27/73
—
DMF
MeCN
CH2Cl2
CHCl3
toluene
6
2
24f
24f
0
—
aReaction conditions: 1a (0.106 g, 1 mmol), lnCl3 (11 mg, 0.05 mmol),
Al (0.108 g, 4 mmol), TMSCI (0.5 mL, 4 mmol), THF (10 mL), rt, N2.
bThe time for 100% conversion of 1a. The formation of 0.5 mmol of
2a corresponds to 100% yield.
cIsolated yield.
dDetermined by 1H NMR.
eThe conversion was not determined.
fNo reaction.
SCHEME 1

Indium-Catalyzed Reductive Coupling of Aromatic Carbonyl Compounds and Imines 311
chlorosilyl)ethane, could be used in the place of
as a reductant, but the catalytic effect of InCl3 was
not observed in the Zn case (Table 4). Results of the
reductive coupling of various aromatic ketones are
summarized in Table 5 where the effect of InCl3 was
generally remarkable.
TMSCl, but the product yield was somewhat lower
with almost the same diastereoselectivity. From all
these experiments, we decided the optimum condi-
tion for this coupling reaction to be the use of the
combination of TMSCl, Al, cat InCl3 (0.5 mol %), and
THF at room temperature. The results of the appli-
cation of this optimized condition to p-substituted
benzaldehydes are shown in Table 3. In these cases,
although the reaction became slow, the correspond-
ing coupling product was obtained in 50–68% yields.
Without the addition of InCl3, no reaction occurred
in all these cases.
Since Nicholas et al. have reported the enantio-
selective reductive coupling of benzaldehyde using a
stoichiometric amount of a chiral titanium complex
[13], we attempted the above reductive coupling in
the presence of either chiral monophosphine ((R)-
MeO-MOP), diphosphine ((R)-BINAP), diphosphine
oxide ((R)-BINAPO), diphosphinite or bisoxazoline
(iPr-Phebox), but enantioselectivity was not ob-
served in the formation of the dl-isomer.
Reductive Homocoupling of Aliphatic Carbonyl
Compounds and Aromatic Imines
In the cases of aliphatic carbonyl compounds, such
as n-octanal (5a), cyclohexanone (5b), and 3-phen-
ylpropanal (5c), the corresponding 1,2-diols could
not be formed (Table 6). However, ␣,b-unsaturated
carbonyl compounds, such as trans-cinnamaldehyde
(5d) and crotonaldehyde (5e), yielded the corre-
sponding 1,2-diols in moderate yields. Next, we per-
formed the reductive coupling of various aromatic
imines (Scheme 3), typical results of which are sum-
Reductive Homocoupling of Aromatic Ketones
Reductive coupling similarly proceeded with aceto-
phenone (3a) as a substrate to afford 2,3-diphenyl-
2,3-butanediol (4a) in good yield, the use of 3 mol %
InCl3 being revealed to be the best (Scheme 2, Table
4). In this case, the reaction occurred even in the
absence of InCl3 catalyst, but a long induction period
was observed, and also, the product yield was much
lower. Figure 1 shows the relationship between the
reaction time and the isolated yield of 4a in this cou-
pling. Here, Zn and Mg were also revealed to work
SCHEME 2
TABLE 4 Effect of Reductant for Reductive Coupling of
Acetophenone (3a)a
Time
Yield
Entry
Reductant (eq)
Al (4)
(h)b (%) of 4ac dl/mesod
TABLE 3 lnCl3-Catalyzed Reductive Coupling of Aromatic
Aldehydes (1)a
1
2f
3g
4g
5
6
7
8
9
10
24e
18e
8
7
4
29
13
57
58
74
64
51
65
29
45
68/32
74/26
71/29
70/30
62/38
64/36
57/43
49/51
52/48
56/44
Al (4)
Time
(h)b
Isolated
lnCl3 (0.005) ꢁ Al (4)
lnCl3 (0.01) ꢁ Al (4)
lnCl3 (0.03) ꢁ Al (4)
lnCl3 (0.05) ꢁ Al (4)
lnCl3 (0.10) ꢁ Al (4)
Zn (4)
Entry Substrate Product
Yield (%) dl/mesoc
1
1a
1a
1b
1b
1c
1c
1d
1d
2a
2a
2b
2b
2c
2c
2d
2d
4
24e
18
61
0
68
0
56
0
50
0
57/43
—
41/59
—
62/38
—
59/41
—
2
2
9
2d
3
4d
5
24e
20
Mg (4)
lnCl3 (0.03) ꢁ Zn (4)
24e
4
6d
7
24e
17
aReaction conditions: 3a (0.12 g, 1 mmol), TMSCI (0.5 mL, 4 mmol),
THF (10 mL), rt, N2.
8d
24e
bThe time for 100% conversion of 3a.
aReaction conditions: 1 (5 mmol), lnCl3 (5.5 mg, 0.025 mmol), Al (0.54
g, 20mmol), TMSCI (2.5 mL, 20 mmol), THF (50 mL), rt, N2.
bThe time for 100% conversion of 1. The formation of 2.5 mmol of 2
corresponds to 100% yield.
cIsolated yield. The formation of 0.5 mmol of 3a corresponds to 100%
yield.
dDetermined by 1H NMR.
eThe conversion was not determined.
cDetermined by 1H NMR.
fUnder sonication in a BRANSONIC ultrasonic cleaner bath, which
delivered a 47 kHz wave, with a fixed electrical power of 125 W.
gFive-fold scale reaction.
dReaction without lnCl3.
eNo reaction.

312 Ohtaka, Mori, and Uemura
TABLE 6 lnCl3-Catalyzed Reductive Coupling of Aliphatic
Aldehydes and Ketonesa
Time Isolated
Entry
Substrate
(h)b Yield (%)c dl/mesod
1
5a
5b
24e
0
—
2
3
24e
18
0
—
—
5c
0f
4
2
27
0
60/40
—
5g
6
5d
5e
2h
3
45
0
64/36
—
7g
2e
aReaction conditions: substrate (1 mmol), lnCl3 (6.6 mg, 0.03 mmol),
Al (0.108 g, 4 mmol), TMSCI (0.5 mL, 4 mmol), THF (10 mL), rt, N2.
bThe time for 100% conversion of 5.
FIGURE 1 Yield of 4a in the Coupling of Acetophenone in
the Presence (ꢃ) and Absence (▫) of lnCl3.
cThe formation of 0.5 mmol of 1,2-diol corresponds to 100% yield.
dDetermined by 1H NMR.
eThe conversion was not determined.
f3-Phenylpropanol (23% yield) was obtained.
gReaction without lnCl3.
TABLE 5 lnCl3-Catalyzed Reductive Coupling of Aromatic
Ketones (3)a
hNo reaction.
Time
(h)b
Isolated
Entry Substrate Product
Yield (%)c dl/mesod
1
2e
3
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
3e
3e
3f
4a
4a
4b
4b
4c
4c
4d
4d
4e
4e
4e
4e
4f
4
24f
10
10g
5h
74
29
76
9
62
48
72
0
56
42
91
90
67
34
68/32
62/38
58/42
64/36
61/39
53/47
65/35
—
—
—
—
—
4e
5
6e
7
5h
5
8e
9
5i
6h
10e
11
12e
13
14e
6h
20
24
4
58/42
50/50
3f
4f
48h
SCHEME 3
aReaction conditions: 3 (1 mmol), lnCl3 (6.6 mg, 0.03 mmol), Al (0.18
g, 4 mmol), TMSCI (0.5 mL, 4 mmol), THF (10 mL), rt, N2.
bThe time for 100% conversion of 3.
cThe formation of 0.5 mmol of 4 corresponds to 100% yield.
dDetermined by 1H NMR.
Plausible Reaction Scheme
eReaction without lnCl3.
Although the precise reaction scheme is not yet clear,
we tentatively propose Scheme 4 for this catalytic
homocoupling by consideration of the generally ac-
cepted scheme for reductive coupling of carbonyl
compounds [14] and also by the known fact of acti-
vation of aluminum by indium ions in chloride so-
lutions [15]. First, a redox-active In–Al alloy might
be formed on the surface of aluminum in the pres-
ence of TMSCl. An electron transfer from the alloy
to aldehydes generates ketyl radicals, and the car-
bon–carbon bond formation takes place by the rad-
ical coupling. When the coupling was attempted in
the presence of m-dinitrobenzene (0.5 equiv to 1a),
fThe conversion was not determined.
gAbout 20% conversion of 3.
hAbout 70–80% conversion of 3.
iNo reaction.
marized in Table 7. In the cases of aromatic aldimi-
nes such as 6a–6f, the effect of InCl3 catalyst (3 mol
%) was remarkable, while, in the cases of aromatic
ketimines such as 6g, the addition of InCl3 decreased
the product yield unexpectedly because of the rapid
decomposition of 6g to the starting ketone (3a),
probably catalyzed by InCl3.

Indium-Catalyzed Reductive Coupling of Aromatic Carbonyl Compounds and Imines 313
TABLE 7 lnCl3-Catalyzed Reductive Coupling of Aromatic
Imines (6)a
plates. Column chromatography was performed
with Merck silica gel 60.
InCl3 was purchased from Aldrich and used
without further purification. Aluminum metal (Al
foil, 0.1 mm ꢄ 0.8 mm) was purchased from Nacalai
Tesque and used without further purification. Chlo-
rotrimethylsilane and THF were distilled before use.
All of the carbonyl compounds were commercially
available and used without further purification. All
of the imines were prepared by the condensation of
carbonyl compounds with amines. The structures of
1,2-diols and 1,2-diamines were determined by com-
parison of spectral data with those of the authentic
samples reported. The structures of 7e and 7g were
determined by analogy with other compounds
[11,16–26].
time
Isolated
Entry Substrate Product (h)b Yield (%)c dl/mesod
1
2e
3
6a
6a
5b
6b
6c
6c
6d
6d
6e
6e
6f
7a
7a
7b
7b
7c
7c
7d
7d
7e
7e
7f
9
12
8
2
6
71
0
36
0
28
0
48
0
63
0
41
0
40
79
45/55
—
43/57
—
42/58
—
42/58
—
4e
5
6e
7
2
2
8e
9
4f
2
38/62
—
10e
11
12e
13
14e
2f
2
g
—
6f
6g
6g
7f
7g
7g
1
2
2
—
50/50
47/53
aReaction conditions: 6 (1 mmol), lnCl3 (6.6 mg, 0.03 mmol), Al (0.108
g, 4 mmol), TMSCI (0.5 mL, 4 mmol), THF (10 mL), rt, N2.
bThe time for 100% conversion of 6.
Typical Procedure for Reductive Homocoupling
of Benzaldehyde (1a) (Table 1, Entry 4)
cThe formation of 0.5 mmol of 7 corresponds to 100% yield.
dDetermined by 1H NMR.
To a mixture of InCl3 (5.5 mg, 0.025 mmol), alumi-
num (0.54 g, 20 mmol), TMSCl (2.5 mL, 20 mmol),
and THF (40 mL) in a 200 mL two-necked flask was
added 1a (0.53 g, 5 mmol) in THF (10 mL) at room
temperature under N2. The mixture was kept at room
temperature with magnetic stirring for 2 hours. Di-
ethyl ether (100 mL) and aqueous HCl (1.2 M, 50
mL) were added to the resulting mixture, and the
organic layer was separated, washed with saturated
aqueous NaHCO3 (50 mL ꢄ 3), dried over Na2SO4,
and concentrated. The residue was purified by col-
umn chromatography on silica gel (eluent, hexane/
ethyl acetate) to obtain 1,2-diphenyl-ethanediol 2a
(325 mg, 1.52 mmol, 61% yield; dl/meso ꢂ 57/43)
and a complex mixture containing benzyl alcohol
and many unidentified compounds (56 mg).
eReaction without lnCl3.
fThe conversion was not determined.
gNot determined.
which is considered to be a radical scavenger, the
product yield was greatly decreased (45% to 5%) (Ta-
ble 1, entry 7), suggesting the intervention of a ketyl
radical species. Finally, metal–oxygen bond cleavage
occurs by the reaction with TMSCl to afford the 1,2-
bis(trimethylsiloxy) derivative of the diol, which
might be hydrolyzed to the product by the work-up
procedure. At this stage, cleavage by the action of a
proton, which may be present in TMSCl in a small
concentration as HCl, might also be operative to
some extent, competitively to afford the diol directly.
In fact, a pH indicator showed the reaction mixture
to be acidic, and also when the coupling of 1a or 3a
was attempted using aqueous HCl in the place of
TMSCl, the product 2a or 4a, respectively, was
formed, although the yield was low (see Experimen-
tal). Since In(O) metal and In(I) compounds were
also effective as catalysts in this system, as recorded
in Table 1, we consider that a similar redox-active
Al–In species might also be formed from these in-
dium compounds and aluminum.
Reductive Homocoupling of Benzaldehyde (1a)
or Acetophenone (3a) in the Presence of HCl in
the place of TMSCl
To a mixture of InCl3 (5.5 mg, 0.025 mmol), alumi-
num (0.54 g, 20 mmol), and THF (30 mL) in a 200
mL two-necked flask were added a THF (10 mL) so-
lution containing HCl (aqueous 35% HCl, 0.5 mL, 5
mmol) and 1a (0.53 g, 5 mmol) in THF (10 mL) at
room temperature under N2. The mixture was kept
at room temperature with magnetic stirring for 24
hours and treated as described previously in a typical
procedure. The product 2a was obtained in 19%
yield (100 mg, 0.467 mmol; dl/meso ꢂ 58/42) to-
gether with benzyl alcohol (60 mg, 0.555 mmol, 11%
yield), and 1a (161 mg, 1.52 mmol) was recovered.
When a similar reaction was carried out using 1
mmol of HCl, no reaction occurred.
EXPERIMENTAL
1H and 13C NMR spectra were measured on JEOL
EX-400, JNM-AL300, and JEOL GSX270 spectrom-
eters for solutions in CDCl3 with Me4Si as an internal
standard. Analytical thin-layer chromatography
(TLC) was performed with Merck silica gel 60 F-254

314 Ohtaka, Mori, and Uemura
SCHEME 4 Plausible reaction scheme.
In the case of the coupling of 3a, using 3a (1
mmol), InCl3 (0.03 mmol), Al (4 mmol), aqueous
35% HCl (0.1 mL, 1 mmol), and THF (10 mL) at
room temperature for 24 hours, 4a was obtained in
55% yield (67 mg, 0.276 mmol; dl/meso ꢂ 58/42),
and 3a (39 mg, 0.330 mmol) was recovered. Simi-
larly, the reaction using 0.2 mmol HCl did not give
any 4a.
1,2-Bis(4-methoxyphenyl)-1,2-ethanediol (dl and
meso) (2d) [16]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 2.10
[2.80] (2H, s, br), 3.75 [3.79] (6H, s), 4.63 [4.72] (2H,
s), 6.73–7.26 (8H, m); 13C NMR (CDCl3, 75.5 MHz) d
ꢂ 55.1 [55.2], 78.7 [77.7], 113.5 [113.6], 128.1
[128.3], 132.0, 159.1 [159.4].
2,3-Diphenyl-2,3-butanediol (dl and meso) (4a)
[16,17]
1,2-Diphenyl-1,2-ethanediol (dl and meso) (2a)
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 1.35
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 2.28
[1.46] (6H, s), 2.23 [2.52] (2H, s, br), 7.06–7.11 (10H,
m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 24.9 [25.1], 78.8
[78.6], 126.9, 127.1 [127.0], 127.3 [127.2], 143.4
[143.7].
[2.91] (2H, s, br), 4.59 [4.72] (2H, s), 7.01–7.23 (10H,
m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 79.0 [78.0],
126.9 [127.0], 127.9 [128.0], 128.2 [128.1], 139.7
[139.8]. The values in brackets are of the meso-iso-
mer. The reported 1H NMR data of the benzylic C–H
hydrogens are 4.59 and 4.72 for dl and meso-isomers,
respectively [16,17].
2,3-Bis(4-chlorophenyl)-2,3-butanediol (dl and
meso) (4b) [18]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 1.39
[1.47] (6H, s), 2.23 [2.55] (2H, s, br), 7.00–7.15 (8H,
m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 24.7 [25.0], 78.5
[78.2], 127.3 [127.3], 128.8 [128.4], 133.1 [133.0],
141.7 [142.2].
1,2-Bis(4-chlorophenyl)-1,2-ethanediol (dl and
meso) (2b) [16]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 2.55
2,3-Bis(4-bromophenyl)-2,3-butanediol (dl and
meso) (4c) [16]
[3.10] (2H, s, br), 4.56 [4.78] (2H, s), 6.97–7.32 (8H,
m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 78.4 [77.1],
128.2, 128.3, 133.8, 137.7 [137.9].
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 1.38
[1.46] (6H, s), 2.05 [2.35] (2H, s, br), 6.94–7.30 (8H,
m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 24.6 [25.0], 78.4
[78.2], 121.4 [121.2], 129.2 [128.8], 130.2 [130.3],
142.2 [142.7].
1,2-Bis(4-methylphenyl)-1,2-ethanediol (dl and
meso) (2c) [16]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 2.22
2,3-Bis(4-methylphenyl)-2,3-butanediol (dl and
meso) (4d) [18]
[2.26] (6H, s), 2.07 [2.77] (2H, s, br), 4.57 [4.65] (2H,
s), 6.95–7.18 (8H, m); 13C NMR (CDCl3, 75.5 MHz) d
ꢂ 21.1 [21.1], 78.8 [78.0], 126.8 [127.0], 128.8
[129.0], 137.0, 137.4 [137.8].
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 1.44
[1.51] (6H, s), 2.26 [2.52] (2H, s, br), 2.32 [2.31] (s,

Indium-Catalyzed Reductive Coupling of Aromatic Carbonyl Compounds and Imines 315
6H), 7.04–7.11 (8H, m); 13C NMR (CDCl3, 75.5 MHz)
d ꢂ 20.9, 25.0 [25.2], 78.7 [78.5], 127.3 [126.8], 127.8
[128.0], 136.5 [136.3], 140.5 [140.9].
[63.4], 114.1 [113.7], 118.6 [118.3], 128.6 [128.6],
128.7 [128.8], 129.2 [129.3], 133.3 [133.5], 138.2
[136.5], 146.4 [145.9].
N,Nꢅ-Diphenyl-1,2-bis(4-methylphenyl)-1,2-
ethanediamine (dl and meso) (7c) [23]
1,1,2,2-Tetraphenyl-1,2-ethanediol (4e) [17]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 2.96
White solid; 1H NMR [CDCl3 ꢁ D2O (few drops), 400
MHz] d ꢂ 2.27 [2.28] (6H, s), 4.52 [4.90] (2H, s),
6.50–7.08 (m, 18H); 13C NMR [CDCl3 ꢁ D2O (few
drops), 75.5 MHz] d ꢂ 21.0, 63.3 [61.5], 114.0
[113.6], 117.8 [117.6], 127.2 [127.4], 129.0 [128.9],
129.1 [129.1], 147.1 [146.5].
(2H, s, br), 7.05–7.25 (20H, m); 13C NMR (CDCl3, 75.5
MHz) d ꢂ 83.0, 126.9, 127.3, 128.6, 144.1.
2,3-Bis(2-naphthyl)-2,3-butanediol (dl and
meso) (4f) [19]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 1.54
[1.61] (6H, s), 2.35 [2.75] (2H, s, br), 7.15–7.77 (14H,
m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 25.2 [25.5], 79.2
[78.8], 125.5, 125.8 [125.8], 125.9, 126.4, 126.7,
127.3, 128.3, 132.3 [132.4], 141.0, 141.0.
N,Nꢅ-Bis(4-chlorophenyl)-1,2-diphenyl-1,2-
ethanediamine (dl and meso) (7d) [24]
White solid; 1H NMR [CDCl3 ꢁ D2O (few drops), 400
MHz] d ꢂ 4.49 [4.88] (2H, s), 6.40–7.19 (18H, m); 13
C
NMR [CDCl3 ꢁ D2O (few drops), 75.5 MHz] d ꢂ 63.8
[61.8], 115.2 [114.9], 122.8 [122.5], 127.2 [127.3],
127.7 [127.7], 128.4 [128.3], 128.9 [128.9], 139.1,
145.4 [144.8].
1,6-Diphenyl-1,5-hexadiene-3,4-diol [20]
White solid; dl-isomer: 1H NMR (CDCl3, 400 MHz) d
ꢂ 4.27 (2H, d, J 5.86 Hz), 6.26 (2H, dd, J 5.86 Hz,
15.9 Hz), 6.71 (2H, d, J 15.9 Hz), 7.22–7.38 (14H, m);
13C NMR (CDCl3, 75.5 MHz) d ꢂ 75.8, 126.6, 127.0,
N,Nꢅ-Bis(4-methylphenyl)-1,2-diphenyl-1,2-
ethanediamine (dl and meso) (7e) [25]
1
127.9, 128.6, 132.7, 136.4. meso-isomer; H NMR
(CDCl3, 400 MHz) d ꢂ 4.43 (2H, d, J 6.11 Hz), 6.28
(2H, dd, J 6.11 Hz, 15.6 Hz), 6.69 (2H, d, J 15.6 Hz),
7.22–7.38 (14H, m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ
75.7, 126.6, 127.0, 127.6, 128.6, 133.1, 136.4.
White solid; 1H NMR [CDCl3 ꢁ D2O (few drops), 400
MHz] d ꢂ 2.14 [2.15] (s, 6H), 4.49 [4.91] (2H, s),
6.40–7.19 (18H, m); 13C NMR [CDCl3 ꢁ D2O (few
drops), 75.5 MHz] d ꢂ 20.3, 64.2 [62.1], 114.2
[113.8], 127.2 [126.9], 127.3 [127.4], 127.4 [127.5],
128.3 [128.2], 129.5 [129.7], 140.1 [138.4], 144.8
[144.2].
2,6-Octadiene-4,5-diol (dl and meso) [11]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 1.66–
1.74 (6H, m), 2.94 (2H, s, br), 3.88 [4.04] (2H, m),
5.35–5.50 (2H, m), 5.63–5.79 (2H, m); 13C NMR
(CDCl3, 75.5 MHz) d ꢂ 17.8 [17.8], 75.7 [75.5], 128.9
[129.1], 129.7 [129.5].
N,Nꢅ-Dibenzyl-1,2-diphenyl-1,2-ethanediamine
(dl and meso) (7f) [21]
1
White solid; H NMR (CDCl3, 400 MHz) d ꢂ 3.42
(4H, AB system, JAB 13.7 Hz), 3.76 (2H, s), 6.96–7.30
(20H, m); 13C NMR (CDCl3, 75.5 MHz) d ꢂ 50.9, 67.1,
126.6, 127.6, 127.9, 128.2, 128.3, 128.6, 140.3, 140.7.
N,Nꢅ-Diphenyl-1,2-diphenyl-1,2-ethanediamine
(dl and meso) (7a) [21,22]
White solid; 1H NMR [CDCl3 ꢁ D2O (few drops), 400
MHz] d ꢂ 4.54 [4.96] (2H, s), 6.49–7.23 (20H, m); 13
C
2,3,N,Nꢅ-tetraphenyl-2,3-butanediamine (dl and
meso) (7g) [26]
NMR [CDCl3 ꢁ D2O (few drops), 75.5 MHz] d ꢂ 63.9
[61.9], 114.2 [113.7], 118.2 [117.8], 127.5, 127.3
[127.5], 128.3 [128.2], 129.0 [129.2], 139.7, 146.8
[146.4].
White solid; 1H NMR [CDCl3 ꢁ D2O (few drops), 400
MHz] d ꢂ 1.64 [1.81] (6H, s), 6.17–7.56 (20H, m); 13
C
NMR [CDCl3 ꢁ D2O (few drops), 75.5 MHz] d ꢂ 20.8,
116.2, 127.4, 127.6, 128.2, 128.5, 128.6, 128.9, 141.2,
145.4.
N,Nꢅ-Diphenyl-1,2-bis(4-chlorophenyl)-1,2-
ethanediamine (dl and meso) (7b) [23]
REFERENCES
White solid; 1H NMR [CDCl3 ꢁ D2O (few drops), 400
MHz] d ꢂ 4.46 [4.91] (2H, s), 6.49–7.23 (18H, m); 13
C
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