Synthesis of 1,3-dioxo-substituted allenes via copper(I)-catalyzed coupling of α-oxo-alkynes and α-oxo-diazos by controlling the sequence of adding substrates

Article abstract of DOI:10.1016/j.tetlet.2019.01.015

A novel direct synthesis of 1,3-dioxo-substituted allenes was developed by copper(I)-catalyzed coupling of α-oxo-alkynes and α-oxo-diazos. It was a sequence of adding substrates-controlled method and the desired products were synthesized chemoselectively by adding α-oxo-alkyne terminally.

Full text of DOI:10.1016/j.tetlet.2019.01.015

Accepted Manuscript
Synthesis of 1,3-dioxo-substituted allenes via copper(I)-catalyzed coupling of
α-oxo-alkynes and α-oxo-diazos by controlling the sequence of adding sub-
strates
Chulong Liu, Yunxiang Weng, Xiaobao Zeng, Weiping Zheng, Xinyan Wang,
Yuefei Hu
PII:
S0040-4039(19)30026-7
https://doi.org/10.1016/j.tetlet.2019.01.015
TETL 50548
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
15 November 2018
13 December 2018
8 January 2019
Please cite this article as: Liu, C., Weng, Y., Zeng, X., Zheng, W., Wang, X., Hu, Y., Synthesis of 1,3-dioxo-
substituted allenes via copper(I)-catalyzed coupling of α-oxo-alkynes and α-oxo-diazos by controlling the sequence
of adding substrates, Tetrahedron Letters (2019), doi: https://doi.org/10.1016/j.tetlet.2019.01.015
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Synthesis of 1,3-dioxo-substituted allenes via
copper(I)-catalyzed coupling of -oxo-alkynes
and -oxo-diazos by controlling the sequence of
adding substrates
Leave this area blank for abstract info.
Chulong Liu,a Yunxiang Weng,a Xiaobao Zeng,a Weiping Zheng,a Xinyan Wang,a* Yuefei Hua*
R2
R2
CuI (10 mol%)
MeCN, rt, 3 h
21 exapmles
O
O
R = alkyl or alkoxyl
R1
R1
R1 = alkoxyl or 2o amino
R2 = H, alkyl or aryl
+
N2
•
R
R
O
O
in 61-80% yields
2

1
Tetrahedron Letters
Synthesis of 1,3-dioxo-substituted allenes via copper(I)-catalyzed coupling of -
oxo-alkynes and -oxo-diazos by controlling the sequence of adding substrates
Chulong Liu,a Yunxiang Weng,a Xiaobao Zeng,a Weiping Zheng,a Xinyan Wang,a* Yuefei Hua*
a Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing
100084, P. R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A novel direct synthesis of 1,3-dioxo-substituted allenes was developed by copper(I)-catalyzed
coupling of -oxo-alkynes and -oxo-diazos. It was a sequence of adding substrates-controlled
method and the desired products were synthesized chemoselectively by adding -oxo-alkyne
terminally.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
allenes
copper catalyst
cross-coupling
alkynes
diazo compounds
Due to the unique scaffold of allene, numerous allenes showed
biological activities and were widely used as building blocks in
organic synthesis.[1] An allene substituted by electron-
withdrawing-groups (EWGs) has at least two advantages: (a) the
electrophilicity of the central carbon and the electron-deficiency
of the double bonds can be enhanced significantly; (b) the
functionalized products can be synthesized easily. As shown in
Figure 1, 1-keto-3-allenecarboxylates 1 and 1,3-allenedicar-
boxylates 2 are two such typical allenes. Based on their
electrophilic or nucleophilic additions and Diels-Alder reactions,
many structurally novel natural products[2] and heterocycles[3]
have been synthesized.
synthetic methods, the precursors 3-5 bearing the same carbon
numbers as the target products 1-2 must be premade by multi-
step syntheses.
a5
b6
c2f
O
Cl
O
RO
RO
R
OR1
OR1
O
O
O
O
OR1
•
DMC
O
RO
RO
OR1
O
O
O
3
2
DMC
O
O
O
O
O
O
O
R
R
OR1
OR1
OR1
OR1
O
O
O
OR1
OR1
OR1
4
•
•
•
O
R
R
RO
O
d2b,3d
OH
O
O
O
1
1
2
R
5
Figure 1. The structures of allenes 1 and 2.
Scheme 1. Conventional methods for synthesis of 1 and 2.
However, in the past decades, the synthetic methods for
allenes 1 and 2 were underdeveloped compared to other allenes.[4]
As shown in Scheme 1a-b, the conventional methods used today
for the synthesis of allenes 2 by dehydration of 3-oxo-1,5-
pentanedioates 3 were developed twenty years ago.[5,6] Although
allenes 1 are very attractive synthons, their synthesis by
dehydration of 3,5-dioxopentanoates 4 normally suffered from
low efficiency due to the low chemoselectivity between two
keto-carbonyls (Scheme 1c).[2f] The oxidation of 5-hydroxy-2-
pentynoate 5 provided an alternative approach, in which the
initially produced 5-oxo-2-pentynoates can be tautomerized to
thermodynamically stable allenes 1 even in acidic conditions
(Scheme 1d).[2b,3d] Since all these methods belong to the linear
Herein, we report a direct method for synthesis of allenes 1
and 2 by a copper(I)-catalyzed cross-coupling between -oxo-
alkynes 6 and -oxo-diazos 7 under mild conditions (Scheme 2).
The efficiency and chemoselectivity of this method were simply
controlled by adding -oxo-alkynes 6 terminally.
R2
R2
CuI (10 mol%)
MeCN, rt, 3 h
O
O
R1
R1
+
N2
•
R
R
O
O
6
7
1 and 2
Scheme 2. Our new method.
1

2
Tetrahedron
In 2004, Fu[7] reported a copper(I)-catalyzed coupling of
Table 1. Effects of catalysts on the yields of 1a and 8a.a
terminal alkynes and -diazoacetates for the synthesis of 3-
alkynyl butyrates under mild conditions (Scheme 3a). In 2013,
Maruoka[8] employed Fu’s method directly to synthesize a group
of 1,3-allenedicarboxylates 2 (Scheme 3b). To our surprise, since
then these two methods almost have not been used for the
synthesis of the allenes 1 and 2 in literature.
O
O
O
7a, cat., MeCN
O
OEt
+
rt, 3 h
•
OEt
O
HN
N
6a
1a
8a
entry
Catalyst (mol%)
CuI (5)
1a (%)b
62
8a (%)b
25
31
35
38
45
30
21
17
1
2
3
4
5
6
7
8
9
CuI (5 mol%)
MeCN, rt, 12 h
CuBr (5)
CuCl (5)
CuCN (5)
CuOAc (5)
CuI (3)
CuI (10)
CuI (15)
---
5
OR1
OR1
trace
trace
trace
55
65
61
a.
b.
R
+
N2
R = alkyl, aryl
R
O
O
O
O
R2
R2
CuI (20 mol%)
OR1 MeCN, rt, 24 h
R = alkoxyl
O
OR1
+
N2
•
R
RO
0
65
O
6
7
2
a To a solution of a catalyst and 7a (1 mmol) in CH3CN (2 mL)
was added 6a (1 mmol) and the mixture was stirred at room
temperature for 3 h. b Isolated yields.
Scheme 3. Fu’s method and Maruoka’s method.
When we tried to use Fu's method to couple 3-butyn-2-one
(6a) with ethyl diazoacetate (7a), the yield of product ethyl 5-
oxo-2,3-hexadienoate (1a) varied widely (0-63%) from person to
person. Thus, we assumed that the mechanisms for the methods
in Scheme 3 may have not been clearly understood and solving
this problem may lead to a general method for the synthesis of
allenes 1 and 2 from easily accessible -oxo-alkynes 6 and -
oxo-diazos 7. Since the substrates and conditions used in these
methods are very simple, we hypothesized that the problems may
be caused by the sequence of adding substrates. Thus, three tests
were made as shown in Scheme 4: (a) under the solvent-free
conditions, a cycloadduct ethyl 5-acetylpyrazole-3-carboxylate
(8a) was obtained in 92% yield within two minutes from 6a and
7a with or without CuI. This result is in agreement with the
reference[9] that the cycloaddition of an electron-poor alkyne and
an -diazoacetate is an easy process; (b) by adding 7a into the
mixture of 6a and CuI in CH3CN, 1a was obtained in 16% yield
accompanied by 8a in 38% yield; (c) by adding 6a into the
mixture of 7a and CuI in CH3CN, the coupling reaction was
finished within 3 h to give 1a and 8a in 62% and 25% yields,
respectively.
As shown in Table 2, CH3CN proved to be the best solvent for
this coupling among all tested coordinative solvents (entries 1-4).
As was expected, the yield of 1a was increased and the yield of
8a was decreased by diluting the solutions (entries 5-7). The best
results were obtained when 4 mL of CH3CN were used (entry 6).
o
No improvements were observed when the reaction ran at 0 C
(entry 8), but the yield of 1a was decreased significantly when
the reaction ran at 40 oC (entry 9).
Table 2. Effects of solvents on the yields of 1a and 8a.a
entry
Solvent
(mL)
NMP (2)
temp
(oC)
25
25
25
25
25
25
25
time
(h)
3
3
3
3
1
3
3
1a
(%)b
22
40
45
65
68
71
71
8a
(%)b
42
35
33
21
17
10
9
1
2
3
4
5
6
7
8
9
DMF (2)
n-PrCN (2)
CH3CN (2)
CH3CN (3)
CH3CN (4)
CH3CN (5)
CH3CN (4)
CH3CN (4)
0
40
3
3
71
43
9
39
a To a solution of CuI (10 mol%) and 7a (1 mmol) in CH3CN was
added 6a (1 mmol) and the mixture was stirred for given
temperature and time. b Isolated yields.
O
8a
8a
O
with or without CuI
solvent-free, rt, 2 min
O
OEt
+
a.
b.
c.
N2
OEt
92%
N
HN
O
6a
7a
To generalize this method, the scope of substrates was tested
under the standard conditions. As shown in Scheme 5, by fixing
6a, the corresponding 1a-1i were synthesized in moderate yields
from 7a-7i. Aryl substituted product 1i was produced smoothly
but with low stability (its decomposition was observed within 1
h). When hex-1-yn-3-one (6b) was used as a substrate, the
corresponding 1j-1k were synthesized. Similarly, 1,3-allene-
dicarboxylates 2a-2h were synthesized from the corresponding
propargyl esters and -diazoacetates, whether the two
carboxylates are the same (2a-2b) or different (2c-2h).
Trisubstituted allenes 1e-1i, 1m and 2g-2h were easily
synthesized by using -substituted -diazoacetates. Among
them, the allyl and propargyl substituted products 1d, 1g-1h and
2e are particularly significant to organic synthesis. As was
expected, when 6a reacted with -diazoacetamides 7j and 7k, the
products 9a and 9b were obtained, respectively. Under the
standard conditions, 2a was prepared in 66% yield on a 3 grams
scale.
6a, CuI (5 mol%)
MeCN, rt, 12 h
O
OEt
OEt
OEt
+
N2
•
O
O
O
7a
1a, 16%
38%
7a, CuI (5 mol%)
MeCN, rt, 3 h
O
O
+
•
8a
6a
1a, 62%
25%
Scheme 4. Three conditional tests and results.
The above results strongly supported our hypothesis and also
promoted us to optimize the reaction conditions further. As
shown in Table 1, the tests for different Cu(I)-catalysts (entries 1-
5) indicated that CuI was the only suitable catalyst for this
coupling. The yield of 1a was decreased and the yield of 8a was
increased by decreasing the amounts of CuI (entry 6). The best
results were obtained when 10 mol% of CuI was used (entry 7).
No 1a was obtained in the absence of CuI (entry 9).
2

3
R2
R2
CuI (10 mol%)
MeCN, rt, 3 h
nitrogen. The initial cross-coupling product alkyne 13a was
O
O
R1
R1
formed by an intramolecular alkynyl migration of 11a to give an
intermediate 12a followed by a protonation. Finally, 13a was
tautomerized to the thermodynamically stable allene 1a.
+
N2
•
R
R
O
O
1, R = alkyl, R1 = alkoxyl, R2 = H, alkyl, aryl
2, R = alkoxyl, R1 = alkoxyl, R2 = H, alkyl
9, R = alkyl, R1 = 2o amino, R2 = H
6
7
O
O
OEt
N2
O
7a
OEt
Cu
(I)
10a
11a
Cu(I)
O
O
O
OEt
OiPr
OtBu
•
•
•
O
O
O
O
O
O
O
H+
intramolecular
migration
1a (71%)
1b (70%)
1c (72%)
6a
O
Ph
OEt
CH3CN
O
O
O
O
(CuI)n
Cu(I)
O
OEt
protonation
•
•
•
inactive
polymer
reactive Cu(I)
spieces
12a
OEt
O
O
Cu(I)
1d (69%)
1e (70%)
1f (70%)
p-tolyl
OEt
O
O
O
O
O
OEt
OEt
•
OEt
•
•
O
•
tautomerization
O
O
O
O
O
O
1i (71%)
1g (75%)
1h (61%)
OEt
1a
13a
O
O
O
Scheme 6. Proposed pathway for the formation of 1a.
OEt
OEt
OEt
OEt
•
•
•
nPr
EtO
nPr
O
However, this pathway must be supplemented by three
hypotheses in order to explain all experimental phenomena. First,
Cu(I)-acetylide 10a may be an in situ formed reactive
mononuclear complex (Scheme 7a).[12] The differences by adding
6a early or terminally may be resulted from the formation of
dinuclear or mononuclear Cu(I)-acetylides, respectively.[13,14] By
adding 6a terminally, the in situ formed reactive mononuclear
Cu(I)-acetylide was captured by 7a rather than converting into a
more stable dinuclear Cu(I)-acetylide (Scheme 7b). By adding 6a
early, parts of Cu(I)-species and 6a were converted into inactive
dinuclear Cu(I)-acetylide leading to a low efficient coupling.
This hypothesis was also supported by two more facts: (a) the
mononuclear Cu(I)-acetylide has been proposed as an
intermediate for similar couplings by Wang based on DFT
studies;[15] (b) our further tests showed that the yield of 1a was
further increased when 6a was added through a syringe pump
(71% in one portion; 78% for 30 min; and 79% for 60 min).
Secondary, Cu(I)-acetylide 10a may be the real catalyst for the
decomposition of -diazoacetate 7a. Since the reactivity of
Cu(I)-catalyst is significantly influenced by ligands, 10a may not
catalyze the decomposition of those stable diazos. Third, no other
Cu(I)-carbene formed except Cu(I)-acetylide-carbene 11a in this
method. Thus, 11a preferentially carried out an intramolecular
alkynyl migration rather than an intermolecular cyclopropanation
or O–H insertion.
1k (71%)
2a (80%)
1j (76%)
O
O
O
OBut
OEt
•
•
•
tBuO
MeO
tBuO
O
O
2b (67%)
2c (75%)
2d (75%)
O
O
O
OEt
OtBu
OEt
O
•
•
•
O
O
MeO
MeO
O
O
O
N
2e (77%)
2f (74%)
2g (69%)
O
O
OEt
N
•
•
•
tBuO
O
O
O
2h (65%)
9a (74%)
9b (65%)
Scheme 5. The synthesis of the products 1a-1k, 2a-2h and 9a-
9b.
However, many substrates were seriously limited to this
coupling method. For example, PhCOC≡CH mainly carried out a
cycloaddition, possibly because it is
dipolarophile. The diazos, such
CH3COCHN2COCH3, PhCOCHN2COPh and EtO2CHN2CO2Et,
were inert to the coupling and the last three were recovered in
almost quantitative yields. These results may be caused by the
fact that these diazos are too stable[10] to be decomposed by
Cu(I)-catalyst. The fact that the propargyl group in 1h stayed
intact indicated that -oxo-alkynes have much higher reactivity
than normal alkynes. The most challenge question is why the
a
as
highly reactive
CH3COCHN2,
Cu
a. mononuclear complexes
b. dinuclear complexes
R
R
H
R
R
R
Cu and/or
Cu
Cu
and/or
Cu
Cu
Cu
alkene in 1g stayed intact rather than carrying out
a
Cu
Cu
cyclopropanation? In fact, Fu has also reported[7] that no
cyclopropanation of alkenes and O–H insertion of alcohols were
detected in his work, but without any explanation.
c.
trinuclear complex
Scheme 7. Proposed three different types of Cu(I)-acetylides.
Thus, a possible pathway for the formation of 1a was proposed
as shown in Scheme 6. Initially, a catalytically inactive polymer
(CuI)n was dissociated by CH3CN to generate a catalytically
reactive CuI·CH3CN,[11] which was then coordinated by alkyne
6a to form Cu(I)-acetylide 10a. When 10a was attacked by diazo
7a, it was converted into Cu(I)-carbene 11a with the loss of
In summary, a novel direct synthesis of 1,3-dioxo-substituted
allenes was developed by copper(I)-catalyzed coupling of -oxo-
alkynes and -oxo-diazos. Its chemoselectivity was controlled
simply by the sequence of adding substrates. The mononuclear
Cu(I)-acetylide was proposed as a key intermediate and a real
Cu(I)-catalyst to well explain most of the results and phenomena.
3

4
Tetrahedron
9. Vuluga, D.; Legros, J.; Crousse, B.; Bonnet-Delpon, D. Green Chem.
Since this method was as simple as by adding -oxo-alkynes
terminally,[16] we may expect that it will have widespread
applications in organic synthesis.
2009, 11, 156.
10. Mortén, M.; Hennum, M.; Bonge-Hansen, T. Beilstein J. Org. Chem.
2016, 12, 1590.
11. (a) Zhu, R.; Xing, L.; Wang, X.; Cheng, C.; Su, D.; Hu, Y. Adv. Synth.
Catal. 2008, 350, 1253. (b) Healy, P. C.; Kildea, J. D.; Skelton, B. W.;
White, A. H. Aust. J. Chem. 1989, 42, 79. (c) Healy, P. C.; Kildea, J. D.;
White, A. H. J. Chem. Soc., Dalton Trans. 1988, 1637.
Acknowledgments
12. In literature, Cu(I)-acetylides are commonly represented by a simple
formula RC≡CCu, but in which each alkyne and Cu(I) are coordinated
each other by one (mononuclear), two (dinuclear), or three C–Cu bonds
(trinuclear). The order of stability for these complexes commonly is:
mononuclear < dinuclear < trinuclear. For selected reviews: (a) Wang,
X.; Wang, X.; Wang, X.; Zhang, J.; Liu, C.; Hu, Y. Chem. Rec. 2017, 17,
1231 (for the structures of Cu(I)-acetylides, see: pp 1232–1233). (b)
Meldal, M.; Tornøe, C. W. Chem. Rev. 2008, 108, 2952 (for the
structures of Cu(I)-acetylides, see: pp 2953–2956). (c) Lang, H.; Köhler,
K.; Blau, S. Coord. Chem. Rev. 1995, 143, 113. (d) Nast, R. Coord.
Chem. Rev. 1982, 47, 89.
We gratefully acknowledge financial support from NNSFC
(Nos. 2147210721372142 and 21372142).
References and notes
1. For selected reviews: (a) “Progress in Allene Chemistry,” Guest editors:
Alcaide, B. and Almendros, P., a themed issue of Chem. Soc. Rev. 2014,
43, 2879. (b) Lechel, T.; Pfrengle, F.; Reissig, H.-U.; Zimmer, R.
ChemCatChem 2013, 5, 2100. (c) “Modern Allene Chemistry”, ed.
Krause, N. and Hashmi, A. S. K., Wiley-VCH, Weinheim, 2004, vol. 1
and 2. (d) Hoffmann-Röder, A.; Krause, N. Angew. Chem., Int. Ed. 2004,
43, 1196. (e) Taylor, D. R. Chem. Rev. 1967, 317.
13. Trinuclear Cu(I)-acetylide is excluded from this pathway because the
premade trinuclear Cu(I)-acetylide 9a was inert to couple with 7a. A
reference for similar results, see: Hassink, M.; Liu, X.; Fox, J. M. Org.
Lett. 2011, 13, 2388.
2. For selected recent references: (a) An, C.; Jurica, J. A.; Walsh, S. P.;
Hoye, A. T.; Smith III, A. B. J. Org. Chem. 2013, 78, 4278. (b) Calter,
M. A.; Li, N. Org. Lett. 2011, 13, 3686. (c) Wang, S.; Wu, F.; Rech, J.
C.; Green, M. E.; Balachandran, R.; Horne, W. S.; Day, B. W.;
Floreancig, P. E. J. Am. Chem. Soc. 2011, 133, 16668. (d) Crimmins, M.
T.; Stevens, M. J.; Schaaf, G. M. Org. Lett. 2009, 11, 3990. (e) Smith III,
A. B.; Jurica, J. A.; Walsh, S. P. Org. Lett. 2008, 10, 5625. (f) Yoshino,
T.; Ng, F.; Danishefsky, S. J. J. Am. Chem. Soc. 2006, 128, 14185. (g)
Floreancig, P. E.; Rech, J. C. Org. Lett. 2005, 7, 5175. (h) Cox, C. D.;
Siu, T.; Danishefsky, S. J. Angew. Chem., Int. Ed. 2003, 42, 5625.
14. Trinuclear Cu(I)-acetylide 9a is an insoluble red solid and was
synthesized by our early procedure: Chen, W.; Wang, B.; Liu, N.; Huang,
D.; Wang, X.; Hu, Y. Org. Lett. 2014, 16, 6140.
15. (a) Wang, T.; Wang, M.; Fang, S.; Liu, J.-Y. Organometallics 2014, 33,
3941. (b) Xiao, Q.; Xia, Y.; Li, H.; Zhang, Y.; Wang, J. Angew. Chem.
Int. Ed. 2011, 50, 1114.
16. A typical procedure for synthesis of ethyl 5-oxohexa-2,3-dienoate
(1a). To a stirred solution of CuI (19 mg, 0.1 mmol) and ethyl -
diazoacetate (7a, 114 mg, 1 mmol) in MeCN (3 mL) was added a
solution of but-3-yn-2-one (6a, 68 mg, 1 mmol) in MeCN (1 mL). After
the resultant mixture was stirred at room temperature for 3 h (monitored
by TLC), the solvent was removed by vacuum and the residue was
purified by flash chromatography (silica gel, 20% EtOAc in PE) to give
3. For selected recent references: (a) Han, T.; Wang, Y.; Li, H.-L.; Luo, X.;
Deng, W.-P. J. Org. Chem. 2018, 83, 1538. (b) Miura, H.; Sasaki, S.;
Ogawa, R.; Shishido, T. Eur. J. Org. Chem. 2018, 1858. (c) Bakshi, D.;
Singh, A. Org. Biomol. Chem. 2017, 15, 3175. (d) Liu, F.; Wang, J.-Y.;
Zhou, P.; Li, G.; Hao, W.-J.; Tu, S.-J.; Jiang, B. Angew. Chem., Int. Ed.
2017, 56, 15570. (e) Wang, Y.; Jiang, C.-M.; Li, H.-L.; He, F.-S.; Luo,
X.; Deng, W.-P. J. Org. Chem. 2016, 81, 8653. (f) Li, H.-L.; Wang, Y.;
Sun, P.-P.; Luo, X.; Shen, Z.; Deng, W.-P. Chem. Eur. J. 2016, 22, 9438.
1
110 mg (71%) of the desired product 1a as a yellow oil. H NMR (400
MHz, CDCl3)  6.15 (d, J = 6.0 Hz, 1H), 6.08 (d, J = 6.0 Hz, 1H), 4.26 (q,
J = 7.3 Hz, 2H), 2.30 (s, 3H), 1.50 (t, J = 7.3 Hz, 3H); 13C NMR (100
MHz, CDCl3)  221.3, 195.3, 163.0, 100.4, 92.2, 61.6, 27.4, 14.0.
4. For selected reviews: (a) Torres, Ò.; Pla-Quintana, A. Tetrahedron Lett.
2016, 57 3881. (b) Neff, R. K.; Frantz, D. E. ACS Catal. 2014, 4, 519. (c)
Yu, S.; Ma, S. Chem. Commun. 2011, 47, 5384.
The products 1b-1k, 2a-2h and 9a-9b were prepared by the similar
procedure.
5. (a) Yoshida, M.; Hidaka, Y.; Nawata, Y.; Rudziński, J. M.; Ōsawa, E.;
Kanematsu, K. J. Am. Chem. Soc. 1988, 110, 1232. (b) Bryson, T. A.;
Dolak, T. M. Org. Synth. 1977, 57, 62. (c) Buchi, G.; Carlson, J. A. J.
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Supplementary Material
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Highlights
A new method for the synthesis of 1,3-
1.
dioxo-substituted allenes was developed.
2. It was achieved via CuI-catalyzed coupling of
-oxo-alkynes and -oxo-diazos.
3. Its efficiency was controlled by adding -oxo-
alkyne terminally.
4. The mononuclear Cu(I)-acetylide was proposed
as a real Cu(I)-catalyst.
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