A novel carbonylative decomplexation of alkyne-dicobalt hexacarbonyls: Hyrocarbamoylation of alkynes

Article abstract of DOI:10.1055/s-1999-2740

A novel carbonylative decomplexation of alkyne-dicobalt hexacarbonyls, i.e. hydrocarbamoylation of alkynes, was carried out by reaction of the complexes with 10 equiv, of primary and secondary amines.

Full text of DOI:10.1055/s-1999-2740

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68
LETTER
A Novel Carbonylative Decomplexation of Alkyne-Dicobalt Hexacarbonyls:
Hydrocarbamoylation of Alkynes
a
b
*b
Takumichi Sugihara* , Yoshinari Okada , Masahiko Yamaguchi , Mugio Nishizawa
aFaculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514, Japan
Email: taku@ph.bunri-u.ac.jp
bFaculty of Pharmaceutical Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan
Received 11 March 1999
mediate the hydrocarbamoylation of alkynes. Further-
Abstract: A novel carbonylative decomplexation of alkyne-
dicobalt hexacarbonyls, i. e. hydrocarbamoylation of alkynes, was
carried out by reaction of the complexes with 10 equiv. of primary
and secondary amines.
more, except the Pauson-Khand reaction and the cyclotri-
7
merization of alkynes, there was no report to construct a
carbon-carbon bond on the alkynes complexed with dico-
balt hexacarbonyls directly. Therefore, we started to in-
vestigate this novel carbonylative decomplexation
reaction. Results of the reaction of 1a with cyclo-
hexylamine under various conditions are summarized in
Table 1.
Key words: hydrocarbamoylation, alkyne-dicobalt hexacarbonyl,
carbonylation, decomplexation, amine
It is known that ‘hard’ Lewis bases, such as amines and al-
cohols, on low-valent organotransition metal complexes
1
make the existing ligands labile and reactive. We utilized
this effect for the promotion of the Pauson-Khand
2
reaction by treatment with primary amines and ammo-
3
nia. The intermolecular Pauson-Khand reaction of 1a
with a reactive alkene, such as norbornene, in the presence
of cyclohexylamine proceeded smoothly to give the de-
sired cyclopentenone 2 in a good yield. In contrast, an at-
tempted reaction of an allyl ether resulted in the recovery
of the starting material. It was, however, found that 1a
was converted to an a,b-unsaturated amide 3a in the pres-
ence of the amine (Scheme 1).
Ph
1
0 min
H
H
O
2
cyclohexylamine
3.5 equiv.)
(98%)
When 1.2 equiv. of the amine were used, the desired 3 was
produced in a low yield along with 1,2,4-triphenylbenz-
ene (Entry 1). Increase in the amount of the amine im-
proved the yield (Entries 1, 2, and 5), and use of more than
10 equiv. of the amine under argon atmosphere gave the
satisfactory result (Entry 5). Comparison of Entries 2-4
revealed that the employment of prolonged reaction time
and a carbon monoxide atmosphere did not have an influ-
ence on the reaction. While the decomplexation proceed-
ed at lower temperatures (Entry 6), the desired
hydrocarbamoylation took place at higher temperatures
Co2(CO)6
(
Ph
in 1,2-dichloroethane
83 °C
H
Ph
N
1a
OBn
O
3a
20 min
+
(35%)
OBn
(97%)
Scheme 1
(
Entry 5). Solvents had an influence on the efficiency of
This reaction corresponds to a hydrocarbamoylation of
alkynes, i. e. a novel carbonylative decomplexation of
alkyne-dicobalt hexacarbonyls. Hydrocarbamoylation of
the reaction. Although the use of 1,2-dichloroethane,
which is the best solvent in the primary amine-promoted
Pauson-Khand reaction,3 and 1,2-dimethoxyethane
(
9
such as toluene, benzene, and chlorobenzene (Entries 5, 7,
and 10). Since N-cyclohexylbenzamide was produced in
the reaction in chlorobenzene (Entry 10), the activated co-
4
alkynes has not been well developed and a major contri-
bution in this area is restricted to the nickel catalyzed re-
DME) did not provide satisfactory results (Entries 8 and
), the reaction underwent efficiently in aromatic solvents
5
action. Usually, synthesis of a,b-unsaturated amide from
alkynes was carried out by hydrohalogenation followed
by carbonylative amidation catalyzed by palladium com-
6
plexes. There is no report that cobalt carbonyl complexes
Synlett 1999, No. 6, 768–770 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
A Novel Carbonylative Decomplexation of Alkyne-Dicobalt Hexacarbonyls
769
balt complexes formed from 1a and the amine oxidatively
added to the carbon-chlorine bond of the chlorobenzene.
The best conditions for the hydrocarbamoylation are as
the follow: 10 equiv. of amines in toluene at 110 °C. Since
formation of alkyne-dicobalt hexacarbonyls usually un-
dergoes in quantitative yields, the present reaction demon-
strates that alkynes can be converted into trans a,b-
unsaturated amides in good yields via two steps conver-
sions. We then continued investigation of the scope of the
reaction and the results are summarized in Table 2.
Co (CO)
Ph
2
6
cyclohexylamine
(10 equiv.)
Ph
O
toluene, 130 °C, 2 h
in a sealed tube
4
5 (86%)
H
Ph
N
O
6
not detected
Scheme 2
R2
R3
N
R3
Co2(CO)6
R2
R1
R1
R1
R1
+
N
R4
R4
H
R2
CO
Co CO
R NH
R2
CO
Co CO
R NH
2
2
1
3
O
–CO
–CO
CO
CO
OC Co
OC
OC Co
R2HN
1
7
CO
CO
R1
R1
R3
R4
R2
CO
Co CO
R2
CO
Co CO
R3
reactive alkenes
CO
CO
Co
Co
R2HN
R4
CO
8
R HNCO
9
2
=
vacant coordination site
the Pauson-Khand reaction
R2
R2NH
R1
R1
O
R2
CO
Co CO
R1
R2
R3
CO
R4 10
RH2N Co
RH2N
12
CO 11
decomplexation
R2NH
∆
R1
R1
R2
O
R2N
R2HN
CO
Co CO
R2
CO
Co CO
CO
R2NH
2
R N
CO
Co
H
H
Co
O
NHR
2 14
13
R HN
2
hydrocarbamoylation
The reaction with primary amines having primary or sec-
ondary alkyl groups, such as benzylamine, (R)-1-phenyl-
ethylamine, and cyclooctylamine, proceeded smoothly to
give the corresponding amides in good yields (Entries 1-
R2
RHN
R1
3
). In contrast, when tert-butylamine and diethylamine
were used, the products were obtained in moderate yields
Entries 4 and 6). The steric bulkiness around the nitrogen
3
O
H
Scheme 3
(
atom has an influence on the hydrocarbamoylation. Since
the reaction with aniline did not proceed (Entry 5), the
electron density on the nitrogen atom also played an im-
portant role. Complexes derived from alkyl substituted The proposed mechanisms are shown in Scheme 3. The
alkynes could be converted into the corresponding amides first step of the reaction is considered as the ligand substi-
in good yields by treatment with primary amines (Entries tution reaction of one of the CO in 1 with the amines fol-
7
-13). The reaction of the complex derived from lowed by liberation of the CO to produce the
diphenylacetylene was cumbersome and decomplexation coordinatively unsaturated complex 8. As shown in
proceeded predominantly (Entry 14). When 4 was treated Scheme 1 and 2, alkenes, if present and sufficiently reac-
with cyclohexylamine under the same conditions, 5 was tive, then occupy the vacant coordination site to produce
produced as a sole product with no sign of the formation 9, which undergoes the Pauson-Khand reaction. When re-
of 6 (Scheme 2). In the presence of alkenes at the suitable active alkenes are absent, a second amine coordinates to
position, the Pauson-Khand reaction is faster than the the cobalt to produce 11. Since 11 is unstable due to the
hydrocarbamoylation.
electronic effects of the coordinated amines, the alkyne
ligand is liberated at the ambient temperature and finally
Synlett 1999, No. 6, 768–770 ISSN 0936-5214 © Thieme Stuttgart · New York

7
70
T. Sugihara et al.
LETTER
the decomplexation occurs as shown in Entry 6 in Table
. At higher temperatures, insertion of CO to the cobalt-
amine bond undergoes smoothly to yield 13, and then the
reaction ended up with the formation of the a,b-unsaturat-
ed amide 3.
Organometallic Chemistry II, Vol. 12; Abel, E. W.; Stone, F.
G. A.; Wilkinson, G. Eds.; Elsevier: New York, 1995, p. 703.
1
(f) Geis, O.; Schmalz, H.-G. Angew. Chem. 1998, 110, 955;
Angew. Chem., Int. Ed. Engl. 1998, 37, 911.
(
(
3) Sugihara, T.; Yamada, M.; Ban, H.; Yamaguchi, M.; Kaneko,
C. Angew. Chem. 1997, 109, 2884; Angew. Chem., Int. Ed.
Engl. 1997, 36, 2801.
It is clear that the reaction underwent in regioselective
manner. In carbometallation and acylmetallation reac-
tions, it is known that metals usually prefer to be located
at the a-position of the phenyl group due to the metal-di-
4) For the decomplexation methods of alkyne-dicobalt
hexacarbonyls, see; (a) Seyferth, D.; Nestle, M. O.; Wehman,
A. T. J. Am. Chem. Soc. 1975, 97, 7417. (b) Descoins, C.;
Samain, D. Tetrahedron Lett. 1976, 745. (c) O’Boyle, J. E.;
Nicholas, K. M. Tetrahedron Lett. 1980, 21, 1595.
(d) Nicholas, K. M.; Mulvaney, M.; Bayer, M. J. Am. Chem.
Soc. 1980, 102, 2508. (d) Isobe, M.; Yenjai, C.; Tanaka, S.
Synlett, 1994, 916. (e) Hosokawa, S.; Isobe, M. Synlett, 1995,
8
recting effect of the phenyl susbtituent. Thus, the car-
bamoyl group might be transferred first from the cobalt to
the terminal alkyne carbon to produce 14, in which one of
the cobalt is located on the internal carbon. Subsequent
protonation and decomplexation gives the trans a,b-unsat-
urated amide 3. The mechanisms of reactions of alkyne-
dicobalt hexacarbonyls with amines are currently under
investigation.
1179. (f) Nakamura, T.; Matsui, T.; Tanino, K.; Kuwajima, I.
J. Org. Chem. 1997, 62, 3032. (g) Sugihara, T.; Ban, H.;
Yamaguchi, M. J. Organomet. Chem. 1998, 554, 163.
5) Reppe, W. Justus Liebigs Ann. Chem. 1953, 582, 1.
6) Schoenberg, A.; Heck, R. F. J. Org. Chem. 1974, 39, 3327.
Also see; (a) Cornils, B. L. In New Synthesis with Carbon
Monoxide; Falbe, J. Ed.; Springer-Verlag: Berlin, 1980, p. 1.
(
(
Acknowledgement
(b) Heck, R. F. In Palladium Reagents in Organic Synthesis;
Academic Press: London, 1985. (c) Colquhoun, H. M.;
Thompson, D. J.; Twigg, M. V. Carbonylation-Direct
Synthesis of Carbonyl Compounds; Plenum Press: New York,
This work is supported in part by grants from the Japan Society of
Promotion of Science (No. RFTF 97P00302) and the Ministry of
Education, Science, Sports, and Culture, Japan (No. 09771890).
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(
(
7) (a) Hübel, W.; Hoogzand, C. Chem. Ber. 1960, 93, 103.
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1
(
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Article Identifier:
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Synlett 1999, No. 6, 768–770 ISSN 0936-5214 © Thieme Stuttgart · New York