Direct palladium(0)-catalyzed amination of allylic alcohols with aminonaphthalenes

Article abstract of DOI:10.1016/S0040-4039(02)02861-7

The direct activation of C-O bonds in allylic alcohols by palladium complexes has been accelerated by carrying out the reactions in the presence of titanium reagents. The palladium-catalyzed amination of allylic alcohols using aminonaphthalenes gave N-all

Full text of DOI:10.1016/S0040-4039(02)02861-7

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 1481–1485
Direct palladium(0)-catalyzed amination of allylic alcohols with
aminonaphthalenes
Yi-Jen Shue, Shyh-Chyun Yang* and Hwe-Chen Lai
Graduate Institute of Pharmaceutical Sciences, Kaohsiung Medical University, Kaohsiung 80708, Taiwan, ROC
Received 20 August 2002; revised 6 December 2002; accepted 13 December 2002
Abstract—The direct activation of CꢀO bonds in allylic alcohols by palladium complexes has been accelerated by carrying out the
reactions in the presence of titanium reagents. The palladium-catalyzed amination of allylic alcohols using aminonaphthalenes
gave N-allylic naphthylamines in good yields. The monoallylation products are formed in the main. © 2003 Elsevier Science Ltd.
All rights reserved.
A principal goal of organometallic chemistry is the
catalytic synthesis of organic compounds by using the
chemistry of organic ligands covalently bound to transi-
tion metals. Most organometallic chemistry has focused
on complexes with covalent metalꢀcarbon or
metalꢀhydrogen bonds. The platinum group transition
metals, in particular palladium and rhodium, have been
workhorse elements in many commercialized catalytic
processes that include hydrogenations, hydroformyla-
tions, acetic acid production, and other CꢀC and CꢀH
bond forming processes.1 Although carbonꢀoxygen,
carbonꢀnitrogen, or carbonꢀsulfur bonds are found in
the majority of important organic molecules, catalytic
organometallic chemistry that leads to the formation of
carbonꢀheteroatom bonds is less common than that
forming carbonꢀcarbon and carbonꢀhydrogen bonds.
Moreover, the construction of CꢀN bonds in amines
using this chemistry is not common.2 In large part,
routes to the necessary reactive intermediates for such
catalysis and the fundamental reactions required of
such intermediates are poorly developed. A number of
synthetic methods for the preparation of allylamines
from alkene derivatives have been developed, but these
require severe reaction conditions or several sequential
reactions.3 Transition metal h3-allyl complexes, as well
as transition metal s-alkyl complexes, play important
roles as active species and key intermediates in many
reactions catalyzed by transition metal complexes.4 Pal-
ladium-catalyzed allylation is an established, efficient,
and highly stereo- and chemoselective method for CꢀC,
CꢀN, and CꢀO bond formation, which has been widely
applied to organic chemistry.5 Although halides,6
esters,7 carbonates,8 carbamates,9 phosphates,10 and
related derivatives11 of allylic alcohols have frequently
been used as substrates, there have been only limited
and sporadic reports dealing with the direct cleavage of
the CꢀO bond in allylic alcohols on interaction with a
transition metal complex.12 Successful applications
using allylic alcohols directly in catalytic processes are
even more limited. This apparently stems from the poor
capability of a nonactivated hydroxyl to serve as a
leaving group.13 We have recently reported our
attempts and some successful applications of a process
involving CꢀO bond cleavage with direct use of allylic
alcohols catalyzed by palladium complexes.14 In this
paper, we wish to report a novel catalytic palladium
complex, which mediates amination of allylic alcohols
with aminonaphthalenes.
We treated a mixture of 1-aminonaphthalene (1a, 2.5
mmol) and allyl acetate (2a, 3.0 mmol) in the presence
of Pd(OAc)2 (1 mol%), PPh3 (4 mol%), and molecular
,
sieves (4 A MS) (200 mg) in benzene under nitrogen, at
room temperature for 3 h. N-Allyl-1-naphthylamine
(3a) was formed in only 11% yield (Scheme 1). The
* Corresponding author. Fax: +886(7)3210683; e-mail: scyang@
kmu.edu.tw
Scheme 1.
0040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02861-7

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Y.-J. Shue et al. / Tetrahedron Letters 44 (2003) 1481–1485
reaction, under reflux, increased the yields of products
3a and N,N-diallyl-1-naphthylamine (4a) to 57 and 6%,
respectively (entry 1 in Table 1). Similarly, the direct
amination of allyl alcohol (2b) at 50°C gave 3a in only
9% yield (entry 2). The palladium-catalyzed amination
of allyl alcohol with 1-aminonaphthalene was investi-
gated under various conditions. In the presence of 25
mol% of Ti(OPri)4 at 50°C, the reaction gave 3a in 80%
yield (entry 3). Decreasing the amount of Ti(OPri)4
afforded 3a in only 32% yield (entry 4). Conversely,
increasing the amount of Ti(OPri)4 increased the yields
of products (entry 5). The effect of addition of
Ti(OPri)4 to promote the palladium-catalyzed allylꢀOH
bond cleavage remarkably enhanced both the reaction
rate and yield. The reaction, under reflux, increased the
yields of 3a and 4a to ca. 80 and 17%, respectively
(entry 6). The reaction did not occur in the absence of
the palladium species (entry 7) or phosphine ligand
(entry 8). Titanium reagents such as Ti(OEt)4 (entry 9),
Ti(OBu)4 (entry 10), Ti(OBui)4 (entry 11), and
Ti[O(CH2)17CH3]4 (entry 12) were also effective for the
allylation. TiCl4 (entry 13) did not promote the reaction
to any great extent. It is known that several factors,
such as the solvent and nature of the nucleophile, can
alter the product pattern in metal-catalyzed allylation.15
At 50°C, six solvents were investigated, benzene, tolu-
ene, dioxane, DMF, CH2Cl2, and MeCN, with benzene
and CH2Cl2 giving the best results (entries 3 and 14–
18). A comparative study of different catalysts in ben-
zene was reported. As the catalyst precursor, Pd(OAc)2
(entry 6), Pd(acac)2 (entry 19), PdCl2(MeCN)2 (entry
20), and Pd(OCOCF3)2 (entry 21) showed high catalytic
activity. Other palladium complexes such as Pd(PPh3)4
(entry 22) and PdCl2 (entry 23) were less active and
gave lower yields. Many reports have indicated16 that
chloride ions can strongly influence the catalytic activ-
ity of palladium catalysts, and it seemed reasonable
that this factor might be responsible for the low reactiv-
ity of PdCl2 in the present system. But using Pd(PPh3)4
coordinated with PPh3 as catalyst increased the yield of
products (entry 24).
We also studied the influence of substituents on the
aminonaphthalene on the reactivity of the amination of
allyl alcohol (2b) using Pd(OAc)2, PPh3, and Ti(OPri)4.
The results collected in Table 2 showed that the nature
of the substituent had an influence on the reaction rate
and the product yield. The amination of allyl alcohol
(2b) worked well with aminonaphthalenes containing
electron-donating groups, giving generally high yields
of the corresponding N-allylic compounds. Conversely,
anilines having strong electron-withdrawing groups,
such as the nitro group (entry 5), gave lower chemical
yields. These differences in reactivity could be related to
the nucleophilicity of the corresponding aminonaph-
thalene. 1-Amino-4-nitronaphthalene (1f) gave only
monoallylated product 3f in 70% yield (entry 5); the
lower yield observed may arise from the nature of the
nitro group. The more acidic 1-amino-4-nitronaph-
thalene is probably less reactive in attack on the p-allyl
Table 1. Reaction of 1-aminonaphthalene (1a) with allylic compounds (2a,b)a
Entry
2
Catalyst
Titanium reagent
Solvent
Yield (%)b (3a:4a)
1
2
3
4
5
6
7
8
2a
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
2b
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
PPh3
–
–
Benzene
Benzenec
Benzenec
Benzenec
Benzenec
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
Toluenec
Dioxanec
DMFc
63 (90:10)
9 (100:0)
80 (100:0)
32 (100:0)
92 (99:1)
97 (82:18)
0
Ti(OPri)4
Ti(OPri)4
d
Ti(OPri)4
e
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OEt)4
Ti(OBu)4
Ti(OBui)4
Ti[O(CH2)17CH3]4
TiCl4
Pd(OAc)2
0
9
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(OAc)2-PPh3
Pd(acac)2-PPh3
PdCl2(MeCN)2-PPh3
Pd(OCOCF3)2-PPh3
Pd(PPh3)4
95 (82:18)
94 (84:16)
96 (91:9)
92 (92:8)
8 (100:0)
40 (100:0)
50 (100:0)
3 (100:0)
78 (99:1)
57 (100:0)
89 (92:8)
97 (93:7)
96 (87:13)
40 (100:0)
70 (100:0)
87 (86:14)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
Ti(OPri)4
c
CH2Cl2
MeCNc
Benzene
Benzene
Benzene
Benzene
Benzene
Benzene
PdCl2-PPh3
Pd(PPh3)4-PPh3
a Reaction conditions: 1a (2.5 mmol), 2 (3.0 mmol), Pd catalyst (1 mol%), PPh3 (4 mol%), titanium reagent (25 mol%), and 4 A molecular sieves
(200 mg) in a solvent were refluxed for 3 h.
,
b
Isolated yield.
c Stirred at 50°C.
d 10 mol% of Ti(OPri)4 was used.
e 50 mol% of Ti(OPri)4 was used.

Y.-J. Shue et al. / Tetrahedron Letters 44 (2003) 1481–1485
1483
Table 3. Reaction of 1-aminonaphthalene (1a) with allylic
alcohols (2c–g)a
complex. Increasing the amount of 2b also afforded
only 3f in 84% yield.
The results for amination of a number of allylic alco-
hols 2c–g with 1-aminonaphthalene (1a) using
i
,
Pd(OAc)2, PPh3, Ti(OPr )4 and 4 A MS are summarized
in Table 3. Amination of crotyl alcohol (2c) gave
mixtures of stereo- and regioisomeric aminonaphthal-
enes 5 and 6 in yields of 55 and 38%, respectively (entry
1, in Table 3). These products may all be derived from
the same p-allyl intermediate which can be attacked at
either the C-1 or C-3 position. The 92:8 E/Z ratio of 5
was determined by GC, the product E alkene arising
from the more thermodynamically stable syn p-allyl
complex. The reaction is considered to proceed via
p-allylpalladium intermediates. The loss of the stereo-
chemistry of the starting alcohol 2c is due to a rapid
s = h3 = s interconversion of the p-allyl intermediate
compared to the rate of amination of this intermediate.
We also noticed that the allylic alcohol 2d reacted with
Table 2. Reaction of aminonaphthalenes (1b–f) with allyl
alcohol (2b)a
1a to give mixtures of stereo- and regioisomeric
aminonaphthalenes 7 and 8, as expected from attack of
the aminonaphthalene on the two allylic termini of the
p-allylpalladium species (entry 2). With 2-substituted
alcohol 2e, monoalkylated product was obtained (entry
3). Alcohol 2f which is prone to give the product having
the olefin conjugated with the phenyl group did give
selectively the conjugated product 10, showing that the
phenyl group acts as a regiocontrolling element (entry
4). However, the alcohol 2g with a bulkier substituent
R was found to be less reactive showing a decrease in
the product yield (entry 5).
We studied the extension of this reaction for the con-
struction of benzo[g]quinoxaline. When a mixture of
2,3-diaminonaphthalene (12, 1 mmol) and 2-butene-1,4-
diol (13, 1.2 mmol) was refluxed in the presence of
catalytic amounts of Pd(OAc)2 (0.01 mmol), PPh3 (0.04
i
,
mmol), Ti(OPr )4 (0.8 mmol), and molecular sieves (4 A
MS) (200 mg) in benzene (5 mL), under nitrogen for 3
h, 1,2,3,4-tetrahydro-2-vinylbenzo[g]quinoxaline 14 was
formed in 90% yield (Scheme 2). This cyclization pro-

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Y.-J. Shue et al. / Tetrahedron Letters 44 (2003) 1481–1485
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Scheme 2.
ceeds through tandem allylic substitution reactions
between 2,3-diaminonaphthalene and 2-butene-1,4-diol
via p-allylpalladium intermediates.
We have shown that palladium(0)-catalyzed amination
of allylic alcohols using aminonaphthalenes is a simple
and efficient route for CꢀN bond formation. The addi-
tion of Ti(OPri)4 to promote the palladium-catalyzed
allylꢀOH bond cleavage remarkably enhanced both the
reaction rate and yield. The amination of allylic alco-
hols worked well with aminonaphthalenes, generally
giving good yields of the corresponding N-allylic naph-
thylamines. When the allylic alcohol is unsubstituted
2b, the reaction is relatively fast, and high yields of the
desired products are obtained. If the alcohol (and thus
the p-allyl complex) is substituted, good chemical yields
are still obtained, but the reaction proceeds more
slowly, and mixtures of isomers are obtained.
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Acknowledgements
We gratefully acknowledge the National Science Coun-
cil of the Republic of China for financial support.
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