3,4-Alkadienyl ketones: Via the palladium-catalyzed decarboxylative allenylation of 3-oxocarboxylic acids

Article abstract of DOI:10.1039/c7cc02050c

In this communication, we report a palladium-catalyzed decarboxylative allenylation of benzyl carbonates and tert-butyl carbonates of 2,3-allenols with 3-oxocarboxylic acids. The reaction provides a new and straightforward approach to 3,4-dienyl ketones under mild conditions.

Full text of DOI:10.1039/c7cc02050c

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COMMUNICATION
Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc
first methanofullerene derivatives of Sc
3
N@C2n (2n
=
68 and 80). Synthesis of the
3
N@D5h-C80
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COMMUNICATION
3
,4-Alkadienyl Ketones via the Palladium-Catalyzed
Decarboxylative Allenylation of 3-Oxocarboxylic acids
Received 00th January 20xx,
Accepted 00th January 20xx
a
a,b
Tonghao Zhu and Shengming Ma
DOI: 10.1039/x0xx00000x
www.rsc.org/
In this communication, we will report a palladium-catalyzed metal-catalyzed reaction of 2,3-allenyl compounds with
decarboxylative allenylation of benzyl carbonates and tert-butyl leaving groups and nucleophiles, such as 1,3-dicarbonyl
carbonates of 2,3-allenol with 3-oxocarboxylic acid. The reaction compounds or amines, affording allenes with a nucleophilic
8
8b,9
provides a new and straightforward approach to 3,4-dienyl functionality. Inspired by these previous works and our
ketones under mild conditions.
interest on allene synthesis, we herein report a palladium-
catalyzed intermolecular decarboxylative allenylation of 3-
1
0
Allenes are particularly attractive building blocks in organic
synthesis because of their ability to undergo a variety of
1
transformations. Thus, the development of efficient methods
oxocarboxylic acids for the efficient synthesis of 3,4-
allenones under mild reaction conditions.
Pervious work:
for the synthesis of functional allenes is of high interest. So far,
the methods for the synthesis of allenones, especially 3,4-
dienyl ketones, have not been well established. In general,
they are synthesized stepwise by α-allenylation of 1,3-
dicarbonyl compounds or imines with buta-2,3-dienyl bromide
[Pd]
LG
NuH
Nu
R
R
LG = OAc, OPO(OEt)
2
This work:
2
intermolecular decarboxylative allenylation of 3-oxocarboxylic acid
O
followed by corresponding decarbonylation or hydrolysis;
S
N
2’-type substitution of α-imido lithium organocuprates with
O
[Pd]/L
R'
LG
COOH
diethyl buta-1,3-dien-2-yl phosphonate or 3-(1,3-dioxolan-2-
R
R'
-CO
2
R
yl)-alkyl magnesium bromide with propargylic bromides
3
followed by hydrolysis; S 2 substitution of allenyllithium with
Scheme 1. Palladium-catalyzed nucleophilic allenylation and
intermolecular decarboxylative allenylation to synthesize 3,4-
N
4
4-(1,3-dioxolan-2-yl)-alkyl
bromide
and
hydrolysis; allenones.
dibromomethylation of the acetals of ω-alken-2-ones treated
5
with methyllithium or magnesium; sequential 1,2-addition of
Our investigation began with the reaction of nona-1,2-
carbon nucleophiles to
fragmentation and
- elimination. In addition, oxidation of the Initially, we optimized the reaction condition by screening
alka-4,5-dienols may produce the corresponding 3,4-allenyl different ligands combined with Pd (dba) ·CHCl as catalyst
β
-carbonyl cyclohexenol triflates, C-C dien-4-yl acetate 1a and 3-phenyl-3-oxopropanoic acid 2a.
6
β
2
3
3
4
,7
t
o
ketones. All these methods suffer from multi-steps and not- and LiOBu as base in THF at 25 C (Table 1, Entries 1-8). We
really-available starting materials. Thus, there is an urgent found that L8 was the best ligand of this reaction, which
demand for the development of a convenient and efficient afforded the decarboxylated product 3aa in 55% NMR yield
synthesis of 3,4-allenones under mild conditions from really (Table 1, Entry 8). The normal expected product 3aa’ was not
available starting materials.
detected in the crude reaction mixture. Although the yield of
Recently, much attention has been paid to the transition 3aa with ligand L7 (54%, Table 1, Entry 7) was slightly lower
1
1
than L8, it was far cheaper, so we chose L7 as the ligand for
further optimization. Further screening of other palladium
sources (Table 1, Entries 9-12), such as [Pd(π-cinnamyl)Cl]2,
a.
b.
Department of Chemistry, Fudan University, 220 Handan Lu, Shanghai 200433, P.
R. China..
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032, P. R.
China
[Pd(allyl)Cl] , Pd(OAc)
2
2
and Pd(PPh
3
)
4
,
showed that
Pd (dba) ·CHCl is still the best.
3
2
3
†
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See the catalyst and 2.0 equiv. of LiOBu as the base, subsequent
DOI: 10.1039/x0xx00000x
Footnotes relaꢀng to the ꢀtle and/or authors should appear here.
2 3 3
Using 2.5 mol% Pd (dba) ·CHCl and 10 mol% binap (L7) as
t
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COMMUNICATION
Journal Name
a
Table 1. Effect of catalyst and ligand.
almost completely recycled(Table 4, Entries 12 and 13).
However, the the amount of 2a was increased to 1.5
equivalent of 1e, the NMR yield of decarboxylated product 3aa
was decreased to 68%(Table 4, Entry 14).
a
Table 2. Effect of base and solvent.
Yield of
Recovery
of 1a (%)
Entry
[Pd] (mol%)
L
b
b
3
aa(%)
1
2
3
4
5
6
7
8
9
Pd
Pd
Pd
2
2
2
(dba)
(dba)
(dba)
3
3
3
·CHCl
·CHCl
·CHCl
3
3
3
(2.5)
(2.5)
(2.5)
L1
0
69
L2
2
4
43
72
38
0
Yield of
Recovery
of 1a (%)
Entry
Base
Solvent
MeCN
L3
b
b
3
aa (%)
t
t
t
t
t
t
t
t
Pd (dba) ·CHCl (2.5)
L4
9
2
2
2
3
3
3
3
3
3
3
1
2
LiOBu
LiOBu
LiOBu
LiOBu
LiOBu
LiOBu
LiOBu
LiOBu
Li CO
0
34
c
Pd
Pd
(dba)
(dba)
(dba)
·CHCl
·CHCl
(2.5)
(2.5)
(2.5)
L5
23
42
54
55
7
DCM
0
42
0
d
L6
L7
0
3
DMSO
17
21
24
26
27
48
0
Pd
2
·CHCl
3
0
4
2
Et O
<14
5
e
Pd (dba) ·CHCl (2.5)
2
L8
0
3
3
5
MTBE
[Pd(π-cinnamyl)Cl]
[Pd(allyl)Cl]
Pd(OAc)
Pd(PPh
2
(2.5) L7
68
57
55
0
6
Toluene
<15
31
0
1
1
1
0
1
2
2
(2.5)
L7
L7
L7
7
7
1,4-Dioxane
f
2
(5)
(5)
15
49
8
DME
g
3
)
4
9
2
3
THF
48
62
a
Reaction conditions: 1a (0.2 mmol), 2a (1.2 equiv.), Pd catalyst (2.5
10
LiOH·H
2
O
THF
THF
THF
THF
5
t
or 5 mol%), ligand (10 mol%), and LiOBu (2.0 equiv.) in THF (1 mL)
t
1
1
1
1
2
3
NaOBu
complicated
complicated
54
o
b
at 25 C for 12 h. Determined by NMR analysis of the crude using
mesitylene as the internal standard.
t
KOBu
t
LiOBu
0
a
Reaction conditions : 1a (0.2 mmol), 2a (1.2 equiv.),
Pd (dba) ·CHCl (2.5 mol%), binap (10 mol%), and base (2.0
2
3
3
o
b
equiv.) in solvent (1 mL) at 25 C for 12 h. Determined by
NMR analysis of the crude using mesitylene as the internal
c
standard. DCM = Dichloromethane. DMSO = Dimethyl
d
e
sulfoxide. MTBE = Tert-butyl methyl ether. DME = 1,2-
f
g
study on the solvent effect indicated that the reaction in THF Dimethoxyethane. THF = Tetrahydrofuran.
afforded 3aa in 54% NMR yield (Table 2, Entry 13). When Li CO and
LiOH·H O were used, recovery of nona-1,2-dien-4-yl acetate 1a in
2
3
With the optimized conditions in hand, the scope of this
corresponding 48% and 62% NMR yield was observed (Table 2, reaction has been investigated and the results are summarized
2
t
t
1
Entries 9 and 10). However, when NaOBu or KOBu were used, the in Table 4. When R group is n-C H or n-C H and Ar is phenyl,
5
11
6 13
reactions were complicated (Table 2, Entries 11 and 12), and no
the reaction afforded the corresponding products 3aa and 3fa
expected product 3aa was detected.
in 79% yields (Table 4, Entries 1 and 2); moreover, alkyl group
1
R with many synthetically useful functional groups, such as
Further study was directed to the effect of leaving group,
various esters of nona-1,2-dien-4-ol 1a-e were used (Table 3,
Entries 1-4, 11). When the leaving group was OCbz, 3aa could
be afforded in 75% NMR yield (Table 3, Entry 11). When the
reaction was reacted without Pd (dba) ·CHCl and binap, 3aa
OTHP, OBn, C=C bond and C-C triple bond may be
1
accommodated (Table 4, Entries 6-9); R may be also aryl
groups bearing halide, COOMe, CN (1m-r) generating the
corresponding products in 44-62% yields (Table 4, Entries 10-
2
3
3
1
5). For the scope of Ar, synthetically attractive Br (2b) or Cl
was not detected and the 1e was almost completely recycled
Table 3, Entry 5). Inspired by above results, we further
(
2c) could be accommodated (Table 4, Entries 4 and 5),
(
however, it is worth noting that the reaction should be
o
conducted at 50 C; Ar may also be 2-thienyl group (2g), 2-furyl
optimized the loading of catalyst, ligand and base (Table 3,
Entries 6-12), and found that the optimal reaction conditions
involved 2.5 mol% Pd (dba) ·CHCl , 7.5 mol% binap (L7),
group (2h), or 2-naphthyl (2i). Furthermore, we could easily
2
3
3
o
conduct the reaction of 2.2 g (7.5 mmol) of 1f to provide 1.26 g
of 3fa (Table 4, Entry 3). The reaction of tert-butyl dodeca-1,2-
dien-5-yn-4-yl carbonate 1s with 3-(naphthalen-2-yl)-3-
oxopropanoic acid 2i afforded the desired product 3si in 49%
yield (Table 4, Entry 16).
and2.0 equiv. LiOBut in THF at 25 C with OCbz as the best
leaving group (Table 3, Entry 12). When we replaced
.
.
Pd (dba) ·CHCl with Cu(OAc) H O or Ni(OAc) 4H O, the 3,4-
2
3
3
2
2
2
2
alkadienyl ketone 3aa was not be observed and the 1e was
2
| J. Name., 2012, 00, 1-3
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Table 3. Effect of leaving group and the loading of catalyst, ligand, complex
COMMUNICATION
A
undergoes the ligand exchange to form
a
and base.
methyleneallylic palladium(II) 3-oxocarboxylate B. After the
decarboxylation, methyleneallylic palladium(II) enolate
intermediate
C
is formed (see Eq. 2b and 3a). Path B
:
decarboxylation of 3-oxocarboxylic acid
2
occurs under
Recovery
[
Pd]/L/Base
x/y/z)
Yield of
existence of base to form the enolate 2’ first (see Eq. 2c and
Entry
LG
b
of b
(
3aa (%)
54
65
70
72
0
3b), which undergoes the subsequent ligand exchange with
1
(%)
0
complex
A
to form intermediate
C. Reductive elimination
1
2
3
4
5
6
7
8
9
OAc (1a)
2.5/10/2
2.5/10/2
2.5/10/2
2.5/10/2
0/0/2
would give the final product
3
and regenerate the Pd(0)
OCO
2
Me (1b)
8
7
catalyst to complete the catalytic cycle.
Table 4. Synthesis of 3,4-allenyl ketones by decarboxylative
OBz (1c)
a
allenylation of 3-oxoacarboxylic acids.
OBoc (1d)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
OCbz (1e)
0
99
32
15
0
2.5/7.5/1.2
2/8/2
21
60
61
63
70
75
0
1
2
Ar
Yield of
b
3 (%)
Entry
1
LG
OCbz
R
3/12/2
1
2
n-C H (1e)
C H (2a)
79(3aa)
79(3fa)
65(3fa)
67(3gb)
46(3hc)
53(3id)
51(3je)
56(3kf)
62(3la)
48(3mg)
44(3nh)
49(3oa)
59(3pa)
51(3qa)
62(3ra)
49 (3si)
5
11
6
6
6
5
5
5
2.5/7.5/3
2.5/5/2
0
OCbz
OCbz
OCbz
OCbz
OCbz
OCbz
OCbz
OCbz
n-C
n-C
6
6
H
13(1f)
13(1f)
C
C
H
H
(2a)
(2a)
10
0
c
3
H
11
2.5/10/2
5/7.5/2
0
d
4
H(1g)
6 4
4-BrC H (2b)
c
1
2
91
94
0
d
5
BnCH (1h)
4-ClC H (2c)
2
6
4
d
1
3
4
5/7.5/2
0
6
7
8
9
CH
THPO(CH
BnOCH
TMSC≡C(CH
(1m)
(1n)
2
=CH(CH
2
)
8
(1i) 4-CH
(1j) 4-CH
(1k) 3-CH
(1l)
3
OC
6
H
4
(2d)
e
1
2.5/7.5/2
2.5/7.5/2
68
80
2
)
5
3
C
6
H
4
(2e)
(2f)
15
0
2
3 6 4
C H
a
LG = Leaving group, Reaction conditions: 1 (0.2 mmol), 2a (1.2
t
equiv.), Pd dba) ·CHCl (x mol%), Binap (y mol%), and LiOBu (z
2
)
3
C
6
H
5
(2a)
2
3
3
e
o
b
1
1
0
1
OBoc
OBoc
OBoc
OBoc
OBoc
OBoc
OBoc
C
6
H
5
2-thienyl (2g)
2-furyl (2h)
equiv.) in THF (1 mL) at 25 C for 12 hours. Determined by
NMR analysis of the crude using mesitylene as the internal
4-FC
3-BrC
4-BrC
6 4
H
c
standard. Pd
.
2
(dba)
d
O(5 mol%). Pd
3
CHCl
3
(2.5 mol%) was replaced with
.
.
12
13
6
6
H
4
4
(1o)
(1p)
C
6
6
H
5
5
(2a)
(2a)
Cu(OAc)
2
H
2
2
(dba)
3
CHCl
3
(2.5 mol%) was
.
e
O(5 mol%). 1.5 equivalent of 2a
replaced with Ni(OAc)
were used.
2
4H
2
H
C
H
1
1
1
4
5
6
4-CH O CC H (1q)
C H (2a)
3
2
6
4
6
5
3-NCC
CH (CH
6
H
4
(1r)
C
6
H
5
(2a)
To understand the mechanism of the reaction, we tried the
reaction of benzyl deca-1,2-dien-4-yl carbonate 1f with
acetophenone 4a under standard conditions. It was found that
no desired product 3fa was formed (Scheme 2, Eq. 1). When 3-
oxocarboxylic acid 2a was directly stirred in THF,
acetophenone was generated in 5% NMR yield after 12 h
3
2
)
5
C≡C (1s)
(1.0 mmol),
2-naphthyl (2i)
a
Reaction conditions
Pd dba) ·CHCl (2.5 mol%), Binap (7.5mol%), LiOBu (2.0 equiv.)
in THF (5 mL) at 25 C for 12 h. Isolated yield Reaction
conditions: 1f (7.5 mmol), 2a (1.2 equiv.), Pd (dba) ·CHCl (2.5
mol%), Binap (7.5 mol%), LiOBu (2.0 equiv.) in THF (37.5 mL)
:
1
2
(1.2 equiv.),
t
2
3
3
o
b
c
2
3
3
(
Scheme 2, Eq. 2a). However, in the presence of
Pd dba) ·CHCl and binap, acetophenone was generated in 83%
NMR yield with no D-incorporation upon quenched with D
Scheme 2, Eq. 2b). Finally, we found that the reaction of 2a
t
2
3
3
o
d
o
e
at 25 C for 12 h. The reaction was at 50 C. The leaving
group of 1m-s is OBoc instead of OCbz owing to the fact that
the corresponding benzyl carbonates of 2,3-allenol could not
be prepared.
2
O
(
t
with LiOBu alone afforded acetophenone-d
3
in 62% yield and
O (Scheme 2, Eq.
·CHCl and binap
7
5% of D-incorportion upon quenching with D
b). The reaction of acid 2d with Pd (dba)
2
2
2
3
3
In conclusion, we have developed a palladium-catalyzed
decarboxylative allenylation of benzyl carbonates or tert-butyl
carbonates of 2,3-allenols with 3-oxocarboxylic acids. The
reaction provides a new, straightforward approach to 3,4-
dienyl ketones under mild conditions. Due to the esaily
availablity of both starting materials and the catalyst as well as
simple operation, this method will be useful in organic
showed the similar results of 2a, however, its reaction with
t
LiOBu is much slower (Scheme 2, Eq. 3a and 3b).
Based the above results, a plausible mechanism is proposed as
shown in Scheme 3. A methyleneallylic palladium(II) complex
1
2
A
was formed via the oxidative addition of 1 with the Pd(0)
catalyst. Then, there are two possible pathways. Path A: The
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COMMUNICATION
Journal Name
synthesis. Further studies to synthesize asymmetric 3,4-
allenones via this protocol are ongoing in our laboratory.
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0 For recent selected examples, see: (a) C. Li and B. Breit, J. Am.
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Scheme 3. Proposed mechanism
Financial support from National Natural Science Foundation
of China (21232006) and the National Basic Research Program
(
2015CB856600) is greatly appreciated. We thank Mr. Xingguo
Jiang in this group for reproducing the results of 3id 3ra, and
si in Table 4.
,
3
A. Toda, D. Nakane and H. Masuda, Chem. Eur. J. 2015, 21,
929; (g) F. Han, X. Zhang, M. Hu and L. Jia, Org. Biomol.
3
Notes and references
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1
For reviews on the chemistry of allenes, see: (a) Modern
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1 Recent price per gram according to Alfa Aesar Chemicals:
binap (L7) vs. 2,2'-bis(diphenylphosphino)biphenyl (L8) =
1
1
2
94:1545 (in CNY).
2 (a) T. Tsuda, Y, Chujo, S. Nishi, K, Tawara, J. Am. Chem. Soc.
1
2
2
980, 102, 6384; (b) J. Tsuji, I. Minami, Acc. Chem. Res. 1987,
, 140; (c) B. M. Trost, J. Xu, T. Schmidt, J. Am. Chem. Soc.
009, 131, 18343.
0
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