Synthesis of allyl allenes through three-component cross-coupling reaction of N-tosylhydrazones, terminal alkynes, and allyl halides

Article abstract of DOI:10.1002/asia.201300340

Three's a crowd: Tri- and tetrasubstituted allyl allenes can be easily accessed by this Cu^I-catalyzed three-component coupling reaction of N-tosylhydrazones, terminal alkynes, and allyl halides. The reaction proceeds through a mechanism involving copper carbene migratory insertion.

Full text of DOI:10.1002/asia.201300340

COMMUNICATION
DOI: 10.1002/asia.201300340
Synthesis of Allyl Allenes through Three-Component Cross-Coupling
Reaction of N-Tosylhydrazones, Terminal Alkynes, and Allyl Halides
Fei Ye,[a] Mohammad Lokman Hossain,[a] Yan Xu,[a] Xiaoshen Ma,[a] Qing Xiao,[a]
Yan Zhang,*[a] and Jianbo Wang*[a, b]
Dedicated to Professor Irina Petrovana Beleskaya
Allenes have attracted considerable attention in recent
years due to their unique structural features and chemical
properties related to the presence of two perpendicular p
bonds. Allenes can undergo diverse transformations, which
are highly useful in organic synthesis.[1,2] Allene moieties
also exist in many natural products and pharmaceutically
relevant compounds.[3] Over the past decades, enormous ef-
forts have been directed to the development of efficient
methods for the synthesis of allenes.[4–6] The traditional ap-
proach toward allenes is based on SN2’-type displacement of
propargyl alcohol derivatives with organocopper species.[5]
More recently, allene synthesis based on direct coupling of
two simple fragments has been explored.[7–11] In this context,
Crabbꢀ and co-workers in 1979 reported the CuBr-mediated
reaction to form terminal allenes from 1-alkynes and form-
Scheme 1. Allene synthesis through CuI-catalyzed three-component reac-
tion.
aldehyde in the presence of diisopropylamine.[9] Recently,
Ma and co-workers have significantly improved this trans-
formation and expanded the reaction to aldehydes, which
constitutes an efficient synthesis of 1,3-disubstituted al-
lenes.[11] Moreover, axially chiral allenes have been success-
fully synthesized with high enantioselectivity by the same
group with their method.[11g]
We recently reported a different method for allene syn-
thesis by CuI-catalyzed cross-coupling reaction of N-tosylhy-
drazones with terminal alkynes.[12–14] A mechanism involving
a copper carbene migratory insertion process has been pro-
posed to account for these transformations (Scheme 1). In
the proposed catalytic cycle of our previous studies, the last
step is the protonation of a propargyl copper or allenyl
copper intermediate.
We envisioned that such nucleophilic organocopper spe-
cies could also be trapped by carbon electrophiles, instead
of a proton. Herein, we demonstrate that indeed the nucleo-
philic organocopper species can be trapped by allyl halides.
This leads to the development of a three-component reac-
tion of N-tosylhydrazone, terminal alkyne, and allyl halide,
which constitutes an efficient synthesis of tri- and tetrasub-
stituted allenes.[15,16]
At the outset of this investigation, CuI-catalyzed three-
component reaction of N-tosylhydrazone 1a, phenylacety-
lene 2a, and allyl iodide 3a was examined (Table 1). With
1,4-dioxane as the solvent at 908C, the effect of base was
first studied (Table 1, entries 1–3). With NaH as the base,
the reaction was found to give the desired product 4a in
15% yield, while KOtBu and NaHMDS were less effec-
tive.[17] It was also observed that the amount of base slightly
affected the reaction (Table 1, entry 4). Carrying out the re-
action at 1108C could further improve the yield (Table 1,
entry 5). The effect of solvent was then studied (Table 1, en-
tries 6 and 7). The reaction in toluene afforded 4a in dimin-
ished yield, while in MeCN, 4a was formed in only trace
amount. To our delight, adding 20 mol% tetra-n-butylam-
[a] F. Ye, M. L. Hossain, Y. Xu, X. Ma, Q. Xiao, Dr. Y. Zhang,
Prof. Dr. J. Wang
Beijing National Laboratory of Molecular Sciences (BNLMS)
Key Laboratory of Bioorganic Chemistry and Molecular Engineering
of Ministry of Education, College of Chemistry
Peking University, Beijing 100871 (China)
Fax : (+86)10-6275-7248
E-mail: wangjb@pku.edu.cn
[b] Prof. Dr. J. Wang
State Key Laboratory of Organometallic Chemistry
Chinese Academy of Sciences
Shanghai 200032 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300340.
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Yan Zhang, Jianbo Wang et al.
Table 1. Optimization of reaction conditions.[a]
ing and electron-withdrawing groups worked well in this
reaction (Table 2, entries 17–24). The reaction also tolerates
the N-tosylhydrazones bearing naphthyl and furan substitu-
ents (Table 2, entries 25 and 26). Moreover, the reaction
also worked with the N-tosylhydrazones derived from ali-
phatic aldehydes (Table 2, entries 27 and 28).
Entry Base (equiv)
Solvent
Additive (20 mol%) Yield [%][b]
Encouraged by the results, we further explored the possi-
bility of the synthesis of tetrasubstituted allenes with this
three-component coupling reaction. Under slightly modified
1
2
3
4
NaH (3.0)
KOtBu (3.0)
NaHMDS (3.0) dioxane
NaH (4.5)
NaH (4.5)
NaH (4.5)
NaH (4.5)
NaH (6.0)
NaH (6.0)
NaH (6.0)
dioxane
dioxane
–
–
–
–
–
–
–
15
9
trace
22
38
18
trace
40
74
dioxane
dioxane
toluene
MeCN
dioxane TBAB
dioxine
dioxine
reaction conditions with [CuACHTNUGTRNEUNG(MeCN)4]PF6 as catalyst and
5[c]
6[c]
7[c]
8
1,10-phenanthroline as the ligand, the N-tosylhydrazones de-
rived from ketones furnished the desired tetrasubstituted
allene products in moderate to good yields. As summarized
in Scheme 2, the reaction is efficient for a series of ketone-
derived N-tosylhydrazone substrates bearing various sub-
stituents, including a cyclopropyl group (6e). Notably, the
reaction with N-tosylhydrazone derived from cyclic ketones
also afforded the allene product in moderate yield (6h).
To further demonstrate the use of this reaction, a gram-
scale experiment has been carried out under standard reac-
tion conditions. The reaction proceeded smoothly, providing
the allene product in 74% yield (1.37 g, Scheme 3).
9[d]
10[e]
TBAB
TBAB
82
[a] If not otherwise noted, the reaction conditions are as following: 1a
(0.1 mmol), 2a (0.1 mmol), 3a (0.1 mmol), CuI (20 mol%), base, TBAB,
solvent (1.5 mL), 908C for 1 h. [b] Yield of isolated product. [c] Reaction
was carried out at 1108C. [d] 1a:2a:3a=1.5:1.0:1.2; 2a (0.4 mmol); diox-
ane (6 mL). [e] 1a:2a:3a=2.0:1.0:1.5; 2a (0.4 mmol); dioxane (6 mL).
monium bromide (TBAB) could improve the reaction
(Table 1, entry 8). In the investigation of the conditions, we
have found that protonation is
more facile than nucleophilic
attack of the allyl halide by an
allenic intermediate. Therefore,
excess NaH was used to trap
the proton in the reaction
system. Finally, we could obtain
the allene product in acceptable
yields by changing the ratio of
substrates (Table 1, entries 9
and 10).
Having the optimized reac-
tion condition in hand, we then
proceeded to study the sub-
strate scope of this reaction by
using various substituted N-to-
sylhydrazones, terminal alkynes,
and allyl halides (Table 2 and
Scheme 2). The reaction with
allyl bromide and allyl chloride
afforded the expected allene
products in diminished yields,
showing their low reactivity rel-
ative to the corresponding allyl
iodide (Table 2, entries 1–3).
As for the N-tosylhydrazone
substrates, it was observed that
the coupling proceeded well
with these derived from aro-
matic aldehydes, and the reac-
tion was not significantly affect-
ed by the substituents on the ar-
omatic rings. The N-tosylhydra-
Table 2. Copper-catalyzed three-component coupling of various N-tosylhydrazone, terminal alkyne, and allyl
halide.[a]
Entry
1, R1 =
2, R2 =
3, R3 =
Yield [%][b]
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
3a, allyl (X=I)
3b, allyl (X=Br)
3c, allyl (X=Cl)
3a, 2-methylallyl (X=Cl)
4a, 82
4a, 67
4a, 37
4b, 38
4c, 34
4d, 64
4e, 53
4 f, 71
4g, 55
4h, 72
4i, 51
4j, 72
4k, 55
4l, 46
4m, 84
4n, 28
4o, 77
4p, 71
4q, 60
4r, 65
4s, 63
4t, 56
4u, 75
4v, 62
4w, 56
4x, 50
4y, 42
4z, 50
Ph
p-MeC6H4
m-MeC6H4
p-tBuC6H4
p-MeOC6H4
p-F3CC6H4
o-ClC6H4
3-thienyl
3e, 2-vinylcyclohexyl (X=Br)
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
3a
9
10
11
12
13
14
15
16
17
18[c]
19
20
21
22
23
24[c]
25[d]
26
27[e]
28[e]
PhCH2CH2
nBu
THPOCH2CH2
tBu
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
p-ClC6H4
p-BrC6H4
2-benzo[d]ACTHNUGRTNE[NUG 1,3]dioxol
p-Me2NC6H4
p-MeC6H4
m-MeC6H4
p-MeOC6H4
o-MeOC6H4
2-naphthyl
2-furanyl
PhCH2CH2
tBu
[a] Unless otherwise noted, all the reactions were carried with N-tosylhydrazone (0.8 mmol), terminal alkyne
(0.4 mmol), and allyl halide (0.6 mmol), CuI (20 mol%), NaH (2.4 mmol), TBAB (20 mol%) in 1,4-dioxane
zones with both electron-donat- (6 mL), 908C for 1 h. [b] Yield of isolated product. [c] 1,4-dioxane (8 mL). [d] 708C. [e] Without adding TBAB.
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Yan Zhang, Jianbo Wang et al.
Experimental Section
General procedure for the CuI-catalyzed cross-coupling
CuI (0.08 mmol, 15.36 mg), NaH (2.0 mmol, 96 mg, 50% purity) and N-
tosylhydrazone 1 (0.88 mmol) were suspended in dioxane (5 mL) in
a 25 mL Schlenk tube under nitrogen. Then terminal alkyne 2 (0.4 mmol)
and allyl iodide 3 (0.6 mmol) were added. The resulting solution was
stirred at 908C for 1 h. After cooling to room temperature, the resulting
mixture was filtered through a short pad of silica gel, then eluted with
hexane and CH2Cl2. The volatile compounds were removed in vacuo, and
the residue was purified by column chromatography (SiO2, hexane).
Acknowledgements
The project is supported by 973 Program (No. 2009CB825300), Natural
Science Foundation of China (21272010).
Keywords: allenes
·
copper
·
diazo compounds
·
homogeneous catalysis · multicomponent reactions
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Published online: && &&, 0000
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COMMUNICATION
Cross-Coupling Reactions
Fei Ye, Mohammad Lokman Hossain,
Yan Xu, Xiaoshen Ma, Qing Xiao,
Yan Zhang,* Jianbo Wang* &&&& — &&&&
Threeꢀs a crowd: Tri- and tetrasubsti-
tuted allyl allenes can be easily
tosylhydrazones, terminal alkynes, and
allyl halides. The reaction proceeds
through a mechanism involving copper
carbene migratory insertion.
accessed by this CuI-catalyzed three-
component coupling reaction of N-
Synthesis of Allyl Allenes through
Three-Component Cross-Coupling
Reaction of N-Tosylhydrazones,
Terminal Alkynes, and Allyl Halides
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Chem. Asian J. 2013, 00, 0 – 0
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ