Bis-functionalization of 1,3-dienes through 1,4-conjugate addition of amphiphilic bis-π-allyl and related palladium intermediates

Article abstract of DOI:10.1055/s-0033-1340171

Palladium-catalyzed three-component coupling of allylstannane, allyl chloride and a functionalized diene is described. Regioselective 1,4-functionalization of the Michael acceptor 1,3-diene is accomplished by the amphiphilic bis-π-allylpalladium complex.

Full text of DOI:10.1055/s-0033-1340171

LETTER
▌359
letter
Bis-Functionalization of 1,3-Dienes through 1,4-Conjugate Addition of
Amphiphilic Bis-π-Allyl and Related Palladium Intermediates
Bis-Functionalization of 1,3-Dienes
T. V. Baiju,a,b Ajesh Vijayan,a,b Nayana Joseph,b Preethanuj Preethalayam,b K. V. Radhakrishnan,*a,b E. Suresh,c
Yoshinori Yamamoto*d
a
Academy of Scientific and Innovative Research (AcSIR), New Delhi 110001, India
b
Organic Chemistry Section, National Institute for Interdisciplinary Science and Technology (CSIR), Trivandrum 695019, India
Fax +91(471)2491712; E-mail: radhu2005@gmail.com
c
Central Salt and Marine Chemicals Research Institute, CSIR-CSMCRI, Bhavnagar 364021, Gujarat, India
d
WPI-AIMR (Advanced Institute for Materials Research), Tohoku University, Katahira 2-1-1, Aobaku, Sendai 980-8577, Japan
E-mail: yoshi@mail.tains.tohoku.ac.jp
Received: 25.09.2013; Accepted after revision: 25.10.2013
vestigations on asymmetric hydrovinylation of linear and
cyclic 1,3-dienes.11 Very recently, Sigman and co-work-
ers achieved palladium-catalyzed 1,4-addition across the
commodity chemical 1,3-butadiene to afford skipped
Abstract: Palladium-catalyzed three-component coupling of allyl-
stannane, allyl chloride and a functionalized diene is described. Re-
gioselective 1,4-functionalization of the Michael acceptor 1,3-diene
is accomplished by the amphiphilic bis-π-allylpalladium complex.
To the best of our knowledge, this is the first time a functionalized polyene products.12
1,3-butadiene has been used as a Michael acceptor. The scope of the
present strategy is further extended to 1,4-allylation–oxyallylation
of functionalized dienes.
X
Pd
Pd
Ln
Key words: palladium, allylation, allyl complexes, coupling,
Michael addition
Figure 1 π-Allyl and bis-π-allyl palladium complexes
Bis-π-allylpalladium (Figure 1) and related intermediates
show amphiphilic reactivity on reaction with activated
olefins13 and benzynes.14 Inter- and intramolecular reac-
tions of aldehydes, imines and activated olefins with bis-
π-allylpalladium complexes have paved the way toward
the synthesis of a number of highly functionalized organic
molecules.13,15 Recently we have reported the bis-func-
tionalization of isatylidenes by using the bis-π-allylpalla-
dium complex as a facile route toward spiro-indol-2-
ones.16 With the highly conjugated heptafulvene, the bis-
π-allylpalladium complex undergoes 1,8-conjugate addi-
tion leading to bis-functionalized cycloheptatriene deriv-
atives.17 A palladium-catalyzed deconjugative allylation
reaction of 1,3-diene was reported for the first time by
Sato and co-workers.18 Cheng et al. reported the reaction
Strategies for 1,4-functionalization of 1,3-dienes through
classical methods include cycloaddition reactions involv-
ing singlet oxygen,1 and heterodienophiles such as nitroso
compounds2 and azodicarboxylates.3 Cycloadducts are
further transformed into target molecules through suitable
synthetic manipulations. Pioneering work on palladium-
catalyzed 1,4-functionalization of 1,3-dienes was reported
by Backvall and co-workers,4 and transition-metal-cata-
lyzed transformations of 1,3-dienes have attracted the at-
tention of a number of organic chemists.5 Synthetic
transformations of 1,3-dienes using nickel,6 palladium,7
iron,8 and rhodium9 have been reported, and Hilt et al.
have utilized the cobalt-catalyzed 1,4-hydrovinylation of
1,3-dienes for the synthesis of functionalized 1,4-dienes.10
RajanBabu and co-workers have carried out detailed in-
CO2R2
CO2R2
R1
R1
R3
OAc
CO2R2
CO2R2
base, Pd(0)
R3
R1
Pd(PPh3)4
CN
+
R2
Cl
R1
+
Bu3Sn
CN
NC
NC
R2
toluene, r.t., 8 h
Scheme 1 Reports by Sato et al.18 (top) and Cheng et al.19 (bottom)
SYNLETT 2014, 25, 0359–0364
Advanced online publication: 02.12.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1340171; Art ID: ST-2013-B0914-L
© Georg Thieme Verlag Stuttgart · New York

360
T. V. Baiju et al.
LETTER
of a bis-π-allylpalladium complex generated from allyl The reaction was then optimized to establish the best cat-
chloride and allenylstannane with 1,3-diene, which af- alytic conditions (see the Supporting Information). Based
forded 1,2-addition products with exclusive regio- and on these studies, the optimal conditions for the transfor-
chemoselectivity (Scheme 1).19
mation was found to be diene (1.0 equiv.), allyl chloride
(2.0 equiv), allyltributylstannane (2.0 equiv), and 5 mol%
[PdCl2(PPh3)2] in THF (2 mL) at room temperature.
As part of our continuing interest in utilizing the amphi-
philic nature of the bis-π-allylpalladium complex in or-
ganic synthesis, we undertook an investigation of its The substrate scope for the bis-allylation strategy was in-
reactivity with highly functionalized 1,3-butadienes.20 vestigated by utilizing various functionalized 1,3-butadi-
Our preliminary experiments involved the reaction of 1,3- enes. It should be noted that a variety of the highly
butadiene derivative 1a with allyl chloride (2) and allyltri- functionalized 1,3-butadienes derived from substituted
butylstannane (3) in the presence of [PdCl2(PPh3)2] in benzylidine malononitriles (1b–d, 1g and 1h) and hetero-
THF at room temperature (Table 1, entry 1).21 The reac- aryl malononitriles (1e and 1f) can be used in this ap-
tion afforded 1,4-bis-allylated product 4a in 78% yield, proach (Table 1). The use of highly substituted 1,3-
the structure of which was established on the basis of a butadienes makes this method potentially valuable for the
range of spectroscopic techniques.22
synthesis of a number of biologically important targets.
Table 1 Palladium-Catalyzed Bis-Allylation of 1,3-Butadienea
CO2Me
CO2Me
Cl
CO2Me
PdCl2(PPh3)2 (5 mol%)
THF, r.t., 8 h
MeO2C
2
+
CN
R
R
SnBu3
NC
CN
CN
1
3
4
Entry
Substrate
Product
Yield (%)
CO2Me
CO2Me
CO2Me
CN
MeO2C
1
78
CN
NC
CN
MeO
MeO
1a
4a
CO2Me
CO2Me
CN
CO2Me
MeO2C
2
3
69
76
CN
NC
CN
1b
4b
CO2Me
CO2Me
CO2Me
CN
MeO2C
CN
NC
CN
1c
4c
CO2Me
CO2Me
CO2Me
CN
MeO2C
4
49
CN
NC
CN
Cl
Cl
1d
4d
Synlett 2014, 25, 359–364
© Georg Thieme Verlag Stuttgart · New York

LETTER
Bis-Functionalization of 1,3-Dienes
361
Table 1 Palladium-Catalyzed Bis-Allylation of 1,3-Butadienea (continued)
CO2Me
Cl
CO2Me
CN
CO2Me
PdCl2(PPh3)2 (5 mol%)
THF, r.t., 8 h
MeO2C
2
+
R
R
SnBu3
NC
CN
CN
1
3
4
Entry
Substrate
Product
Yield (%)
CO2Me
NC
CO2Me
CN
5
61
71
O
CO2Me
MeO2C
NC
CN
O
1e
4e
CO2Me
NC
CO2Me
CN
CN
6
S
CO2Me
MeO2C
NC
S
1f
4f
CO2Me
CO2Me
CN
CO2Me
MeO2C
7
30
CN
NC
CN
MeO
MeO
OMe
OMe
1g
4g
CO2Me
CO2Me
CO2Me
CN
MeO2C
8
47
CN
NC
CN
1h
4h
a Reaction conditions: 1,3-diene 1 (1.0 equiv), allyl chloride 2 (2.0 equiv), allyl tributylstannane 3 (2.0 equiv), [PdCl2(PPh3)2] (5 mol%), THF
(2 mL), r.t., 8 h.
A plausible mechanistic pathway for bis-allylation is il- The structure of the allylated-oxyallylated product was
lustrated in Scheme 2. The initial event involves oxidative unambiguously confirmed by single-crystal X-ray analy-
addition of allyl chloride 2 to a palladium(0) species to sis of 6b (from the reaction of 1b and 5; Figure 2).23 The
produce the η3-allylpalladium intermediate A. This inter- reaction presumably proceeds through oxidative addition
mediate undergoes ligand exchange with allyltributylstan- of palladium to the diallyl carbonate, followed by loss of
nane 3 to generate bis-η3-allylpalladium intermediate B, CO2 to give intermediate D. Nucleophilic 1,4-addition
which subsequently undergoes nucleophilic 1,4-addition followed by reductive elimination results in the formation
with diene 1 to form intermediate C, which, on reductive of product 6.
elimination, forms 1,4-bis-allylated product 4.
To develop conditions that were suitable for this transfor-
To demonstrate the use of related π-allyl palladium inter- mation, we surveyed a variety of palladium catalysts and
mediates, we initiated our investigations with the al- solvents (see the Supporting Information) and found that
lylation-oxyallylation reaction of 1a and diallylcarbonate the optimal conditions for this reaction were: a mixture of
5 by the use of [Pd(PPh3)4] as the catalyst and THF as the 1,3-diene/diallyl carbonate (1:2) with 5 mol% [Pd(PPh3)4]
solvent. To our delight, the desired allylated-oxyallylated in THF (2 mL) with a reaction time of 8 hours.
product 6a was obtained in 71% yield (Table 2, entry 1).
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 359–364

362
T. V. Baiju et al.
LETTER
CO2Me
CO2Me
CN
Cl
R
Pd (0)
2
NC
4
CO2Me
CO2Me
CN
Pd
A
3
Cl
SnBu3
R
–
CN
+Pd
Bu3SnCl
C
Pd
B
MeO2C
CO2Me
Figure 2 Single-crystal X-ray structure of 6b
R
1
CN
NC
rivatives by a palladium-catalyzed three-component cou-
pling reaction. To the best of our knowledge, this is the
first report on a palladium-catalyzed 1,4-conjugate addi-
tion reaction of 1,3-butadiene derivatives via amphiphilic
bis-π-allylpalladium and related complexes. Further syn-
thetic manipulations of the synthesized trienes and inves-
tigations on the scope of other related palladium
intermediates are under way and will be reported in due
course.
Scheme 2 Mechanistic rationale of palladium-catalyzed bis-al-
lylation of 1,3-butadiene
A detailed study to expand the 1,4-allylation–oxyal-
lylation strategy to other 1,3-dienes (1b–f) was undertak-
en, the results of which demonstrated that a wide range of
substitution patterns are tolerated (Table 2).
In conclusion, we have developed a simple and efficient
strategy for the bis-functionalization of 1,3-butadiene de-
Table 2 Palladium-Catalyzed Allylation–Oxyallylation Reaction of 1,3-Dienesa
CO2Me
CO2Me
Pd(PPh3)4 (5 mol%)
CO2Me
O
O
O
MeO2C
THF, r.t., 8 h
+
CN
O
R
R
NC
CN
PdLn
+
O–
CN
5
1
6
D
Entry
Substrate
Product
Yield (%)
CO2Me
CO2Me
CN
CO2Me
MeO2C
O
1
71
CN
NC
CN
MeO
MeO
1a
6a
CO2Me
CO2Me
CN
CO2Me
MeO2C
O
2
55
CN
NC
CN
1b
6b
Synlett 2014, 25, 359–364
© Georg Thieme Verlag Stuttgart · New York

LETTER
Bis-Functionalization of 1,3-Dienes
363
Table 2 Palladium-Catalyzed Allylation–Oxyallylation Reaction of 1,3-Dienesa
CO2Me
CO2Me
Pd(PPh3)4 (5 mol%)
CO2Me
O
O
O
MeO2C
THF, r.t., 8 h
+
CN
O
R
R
NC
CN
PdLn
+
O–
CN
5
1
6
D
Entry
Substrate
Product
Yield (%)
CO2Me
CO2Me
CN
MeO2C
CO2Me
O
3
66
CN
NC
CN
1c
6c
CO2Me
CO2Me
CO2Me
CN
MeO2C
O
4
31
CN
NC
CN
Cl
Cl
1d
6d
6e
6f
CO2Me
NC
CO2Me
CN
O
5
6
69
43
O
CO2Me
MeO2C
NC
CN
O
1e
CO2Me
CO2Me
NC
CN
O
S
CO2Me
MeO2C
NC
CN
S
1f
a Reaction conditions: 1,3-diene 1 (1.0 equiv.), diallyl carbonate 5 (2.0 equiv.), [Pd(PPh3)4] (5 mol%), THF (2 mL), r.t., 8 h
Acknowledgment
References and Notes
T.V.B., A.V., N.J., and P.P. thank CSIR, New Delhi and UGC for
research fellowships. Financial assistance from the Department of
Science and Technology (DST No: SR/S1/OC-78/2009) and the
Council of Scientific and Industrial Research, New Delhi [12th FYP
project on catalysts for speciality chemicals (CSC-0125)] are
greatly acknowledged. The authors also thank Ms. Saumini
Mathew, Mr. Saran P. Raveendran, and Ms. S. Viji of CSIR-NIIST
for recording NMR and mass spectra, respectively.
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(21) Typical Procedure (Compound 4a): To a degassed
solution of [PdCl2(PPh3)2] (4.4 mg, 0.0064 mmol) in
anhydrous THF (2 mL) in a Schlenk tube, allyltributyl-
stannane 3 (85.2 mg, 0.25 mmol) was added followed by
allyl chloride 2 (19.6 mg, 0.25 mmol). To this, 1a (42.02 mg,
0.12 mmol) was added (in THF) and the mixture was stirred
at room temperature for 8 h. After the completion of the
reaction (as evident by TLC), the solvent was removed under
reduced pressure and the residue was purified by using silica
gel (100–200 mesh) column chromatography (EtOAc–
hexane, 12%) to afford 4a (41.1 mg, 78%).
(22) Spectral Data of 4a: Rf = 0.46 (EtOAc–hexane, 4:6); IR
(neat): 3079, 2955, 2919, 2850, 2313, 2246, 1734, 1604,
1510, 1461, 1376, 1290, 1248, 1177, 1118, 1032 cm–1; 1H
NMR (500 MHz, CDCl3): δ = 7.26–7.24 (m, 1 H), 7.08 (d,
J = 8.5 Hz, 1 H), 6.98–6.94 (m, 2 H), 5.94–5.86 (m, 1 H),
5.56–5.47 (m, 1 H), 5.42–5.35 (m, 2 H), 5.05–4.98 (m, 2 H),
3.89 (s, 3 H), 3.84 (s, 3 H), 3.72 (s, 3 H), 3.18–3.15 (m, 1 H),
2.87–2.75 (m, 2 H), 2.63–2.58 (m, 1 H), 2.27–2.21 (m, 1 H);
13C NMR (125 MHz, CDCl3): δ = 171.0, 166.0, 160.4,
137.4, 136.6, 134.0, 131.1, 130.1, 128.7, 126.0, 123.5,
118.1, 114.5, 114.3, 113.7 (2C), 55.3, 52.6, 52.5, 48.2, 42.7,
42.5, 33.8; HRMS (ESI): m/z [M + Na]+ calcd for
C23H24N2NaO5: 431.15829; found: 431.15646.
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Synlett 2014, 25, 359–364
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