Regioselective Allylmetalation of Allenes with Tetraallylmanganate or Allylmagnesium Chloride under MnCl2 Catalysis

Article abstract of DOI:10.1021/ol035793j

(Equation presented) Treatment of allenes with tetraallylmanganate provides allylated products with high regioselectivity. A catalytic amount of MnCl₂ combined with allylmagnesium chloride also achieves efficient allylmetalatlon of allenes. The resulting alkenylmagnesium spedes react with various electrophiles. In the presence of molecular oxygen, the alkenylmagnesium undergoes diallylation reaction. A cyclization reaction of 1,2,6-heptatriene with tetraallylmanganate is also described.

Full text of DOI:10.1021/ol035793j

ORGANIC
LETTERS
2003
Vol. 5, No. 24
4623-4626
Regioselective Allylmetalation of Allenes
with Tetraallylmanganate or
Allylmagnesium Chloride under MnCl2
Catalysis
Toshihiro Nishikawa, Hiroshi Shinokubo,* and Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto UniVersity,
Kyoto 615-8510, Japan
hshino@kuchem.kyoto-u.ac.jp; oshima@fm1.kuic.kyoto-u.ac.jp
Received September 17, 2003
ABSTRACT
Treatment of allenes with tetraallylmanganate provides allylated products with high regioselectivity. A catalytic amount of MnCl2 combined
with allylmagnesium chloride also achieves efficient allylmetalation of allenes. The resulting alkenylmagnesium species react with various
electrophiles. In the presence of molecular oxygen, the alkenylmagnesium undergoes diallylation reaction. A cyclization reaction of 1,2,6-
heptatriene with tetraallylmanganate is also described.
Carbometalation of carbon-carbon multiple bonds is an
important process in organometallic chemistry from both
theoretical and practical standpoints.1 A variety of unsaturated
substrates such as alkenes and alkynes have hitherto been
employed. However, allenes and their derivatives have
received relatively little attention.2 Alexakis and Normant
reported that organocopper and organocuprate reagents add
to 1-methoxypropa-1,2-diene stereo- and regioselectively.3,4
We have recently demonstrated that tetraallylmanganate
reacts, stereo- and regioselectively, with homopropargylic
alcohol methyl ethers to provide allylmanganation products.5
Here we wish to describe highly regioselective allylmetala-
tion of allenes mediated by tetraallylmanganate.6 We also
report that allylmagnesium chloride efficiently adds to allenes
with high regioselectivity under MnCl2 catalysis.
Treatment of cyclic allene 1a with tetraallylmanganate,
derived from allylmagnesium chloride and manganese(II)
chloride in a 4:1 ratio, furnished allylated product 2a in 69%
yield after aqueous workup (Scheme 1).7 However, the
reaction of 1a with triallylmanganate provides 2a in only
12-15% yield along with regioisomeric product 3 in 18%
yield.
Treatment of terminal allene 1b with tetraallylmanganate
in THF at 0 °C for 20 h afforded 2b in 33% yield
(2) Examples of carbometalation of allenes: (a) Mikhailov, B. M. Pure
Appl. Chem. 1974, 39, 505 (allylboration). (b) Richey, H. G., Jr.; Szucs, S.
S. Tetrahedron Lett. 1971, 12, 3785 (allylmagnesation). (c) Normant, J. F.;
Quirion, J. Ch. Tetrahedron Lett. 1989, 30, 3959. (d) Normant, J. F.; Quirion,
J. Ch.; Alexakis, A.; Masuda, Y. Tetrahedron Lett. 1989, 30, 3955
(allylzincation). (e) Normant, J. F.; Quirion, J. Ch.; Masuda, Y.; Alexakis,
A. Tetrahedron Lett. 1990, 31, 2879 (allylcupration). (f) Araki, S.; Usui,
H.; Kato, M.; Butsugan, Y. J. Am. Chem. Soc. 1996, 118, 4699 (allylin-
dation). (g) Shirakawa, E. Nakao, Y. Hiyama, T. Chem. Commun. 2001,
263 (acylstannylation). (h) Shirakawa, E. Nakao, Y. Tsutimoto, T. Hiyama,
T. Chem. Commun. 2002, 1962 (alkynylstannylation).
(3) Klein, H.; Eijsirga, H.; Westmijze, E.; Meijer, J.; Vermeer, P.
Tetrahedron Lett. 1976, 12, 947.
(4) (a) Alexakis, A.; Normant, J. F. Isr. J. Chem. 1984, 24, 113. (b)
Alexakis, A.; Mangeney, P.; Ghribi, A.; Marek, I.; Sedrani, R.; Guir, C.;
Normant, J. F. Pure Appl. Chem. 1988, 60, 49.
(1) For reviews on carbometalation, see: (a) Normant, J. F.; Alexakis,
A. Synthesis 1981, 841. (b) Oppolozer, W. Angew. Chem., Int. Ed. Engl.
1989, 28, 38. (c) Negishi, E. Pure Appl. Chem. 1981, 53, 2333. (d) Knochel,
P. In ComprehensiVe Organometallic Chemistry II; Able, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol. 11, p 159. (e)
Knochel, P. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming,
I., Eds.; Pergamon: Oxford, 1991; Vol. 4, p 865. (f) Yamamoto, Y.; Asao,
N. Chem. ReV. 1993, 93, 2207. (g) Negishi, E.; Kondakov, D. Y. Chem.
ReV. 1996, 96, 417. (h) Marek, I.; Normant, J. F. In Metal Catalyzed Cross-
Coupling Reactions; Diederich, F., Stang, P., Eds.; Wiley VCH: New York,
1998; p 271.
(5) (a) Okada, K.; Oshima, K.; Utimoto, K. J. Am. Chem. Soc. 1996,
118, 6076. (b) Tang, J.; Okada, K.; Shinokubo, H.; Oshima, K. Tetrahedron
1997, 53, 5061.
10.1021/ol035793j CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/05/2003

equiv) in the presence of MnCl2 (20 mol %) in THF at 25
°C afforded 2c in 76% yield (Table 1, entry 1). The
Scheme 1
Table 1. MnCl2-Catalyzed Allylmagnesation of Various
Allenes
accompanied by unidentified complex side products. The
addition of HMPA increased the yield of 2b up to 53%.8
Quenching the reaction intermediate 4b with D2O provided
the corresponding deuterated product (Scheme 2).
entry allene electrophilea product yield (%)b
E/ Z ratio
1:>99
>99:1
>99:1
ndc
1
1a
1a
1a
1c
1c
1c
1d
1d
1d
1d
1d
H2O
2a
5a
6a
2c
5c
6c
2d
5d
6d
7d
8d
2f
58
40
34
76
62
50
70
63
45
71
47
78
68
57
69
Scheme 2
2
I2
3
CH3COClf
4
H2O
5
I2
23:77
6
CH3COClf
14:86e
ndc
54:46d
62:38e
59:41 or 41:59
ndc
7
H2O
8
I2
9
CH3COClf
CH2dCHCH2Br
PhCHOg
10
11
12
13
14
15
1fh H2O
1fh I2
1fh CH3COClf
1fh CH2dCHCH2Br
Scheme 3 shows other examples of the reaction of various
allenes with tetraallylmanganate. Internal allenes such as 1c
5f
6f
7f
a Electrophiles (4.0 equiv) were employed. b Isolated yield. c Not deter-
mined. d Z/E ratio of product was determined by 1H NMR. e The config-
uration of the product was confirmed by NOESY experiments. f CuCN‚2LiCl
(20 mol %) was added before the addition of acetyl chloride. g The reaction
of 4d with benzaldehyde proceeded at -78 °C for 1.5 h. h In the presence
of HMPA (2.0 equiv).
Scheme 3 a
intermediary alkenylmagnesium species 4, furnished by
MnCl2-catalyzed allylmagnesation, reacted with various
electrophiles (Table 1). The use of water, iodine, allyl
bromide, and aldehyde9 as electrophiles provided the cor-
responding products 2, 5, 7, and 8 in moderate to good yields.
In the case of acetyl chloride, the addition of CuCN‚2LiCl
(20 mol %) improved the yields of R,â-unsaturated ketones
6. It is particularly noteworthy that 1,1-disubstituted allene
1f yielded the corresponding products 2f, and 5f-7f bearing
a quaternary center.
At the present stage, the reaction mechanism, especially
the regiochemical control, is not clear. We illustrate here
our speculation in Scheme 4. The reaction is triggered by
the coordination of tetraallylmanganate to allene. The ab
initio calculation at the B3LYP/6-31G* level indicates that
the HOMO of 1,2-butadiene is developed at the more
b
a Z/E ratio of product was not determined. In the presence of
HMPA (2.0 equiv), 0 °C, 20 h. NMR yield.
c
and 1d afforded the desired products 2c and 2d in good
yields. Terminal allene 1e was smoothly allylated regio-
selectively in the presence of HMPA.
Next, we investigated the catalytic use of MnCl2. An
addition of 1c to a solution of allylmagnesium chloride (3.0
(6) For the use of organomanganate reagents in organic synthesis, see:
(a) Oshima, K. J. Organomet. Chem. 1999, 575, 1. (b) Shinokubo, H.;
Oshima, K. J. Synth. Org. Chem. Jpn. 1999, 57, 27. (c) Shinokubo, H.;
Oshima, K. Catal. SurV. Asia 2003, 7, 39. (d) Hojo, M.; Harada, H.; Ito,
H.; Hosomi, A. J. Am. Chem. Soc. 1997, 119, 5459. (e) Hojo, M.; Harada,
H.; Ito, H.; Hosomi, A. Chem. Commun. 1997, 2077. (f) Hojo, M.; Sakuragi,
R.; Murakami, Y.; Baba, Y.; Hosomi, A. Organometallics 2000, 19, 4941.
(g) Cahiez, G. An. Quimm. 1995, 91, 561. (h) Normant, J. F.; Cahiez, G. In
Modern Synthetic Methods; Scheffold, R., Ed.; Otto Salle Verlag: Frankfurt
am Main, 1983; Vol. 3, p 173.
(8) Other allylic manganates derived from the corresponding Grignard
reagents were studied on the reaction with 1b. The tetramethallylmanganate
reagent provided 4-decyl-2-methylhexa-1,5-diene in only 30% yield.
Treatment of 1b with tetracrotylmanganate afforded a complex mix-
ture.
(9) The reaction of 4 with aldehyde at 0 °C afforded a mixture of the
coupling product and R,â-unsaturated ketone derived from the product.
(7) The reaction of 1a with allylmagnesium chloride in the absence of
MnCl2 did not proceed, and the starting material 1a was recovered
quantitatively.
4624
Org. Lett., Vol. 5, No. 24, 2003

Scheme 4
Scheme 6
cyclized product 10 in 46% yield. The reaction proceeded
diastereoselectively. The stereochemistry of 10 was assigned
by NOESY experiments. An addition of D2O to the reaction
mixture yielded the labeled product with deuterium in-
corporation at the methyl group. In contrast to 9a, 1,2,7-
triene 9b provided none of cyclized products. Instead,
the reaction with 9b afforded allylated product 11 in 71%
yield.11
substituted carbon-carbon double bond. Consequently, the
interaction of manganate reagent with allene provides a
π-complex B rather than A. The allyl group on manganese
then attacks the terminal carbon via path b, evading a steric
repulsion between the coplanar hydrogen atom and the
migrating allyl group.
Diallylation products were formed in the presence of
molecular oxygen.10 A THF solution of 1a was treated with
allylmagnesium chloride (5.0 equiv) in the presence of MnCl2
(20 mol %) under argon atmosphere for 9 h at 25 °C. The
mixture was then exposed to air for 40 h to provide
diallylated product 7a in 64% yield (Scheme 5). In the
We propose the following reaction mechanism for the
enallene cyclization reaction (Scheme 7). An addition of
Scheme 7
Scheme 5
allylmanganate to the allenyl moiety of 9a provides the
alkenylmanganese intermediate 12. The terminal olefin
intramolecularly inserts into the Mn-C bond of 12, yielding
alkylmanganese 13. Finally, quenching of 13 with H2O
furnishes 10. The formation of the alkylmanganese inter-
mediate 13 was indicated by the deuterium labeling experi-
ment (vide supra).
In conclusion, we have demonstrated that allylmanganation
of allenes with tetraallylmanganate proceeded with high
regioselectivity. A catalytic version of allylmetalation of
allenes with allylmagnesium chloride under MnCl2 catalysis
has also been achieved. The resulting alkenylmagnesium
species can be efficiently functionalized upon the treatment
with various electrophiles. In the presence of molecular
oxygen, the alkenylmagnesium undergoes diallylation reac-
reaction mixture, monoallylated product 2a was not detected.
Starting from 1d, the corresponding diallylated product 7d
was obtained in 77% yield.
We next picked up enallene 9 as a substrate in the reaction
with tetraallylmanganate (Scheme 6). Treatment of 1,2,6-
triene 9a with tetraallylmanganate at 0 °C for 22 h afforded
(10) We assume that molecular oxygen oxidizes manganese to a higher
oxidation state, facilitating reductive elimination from alkenylallylmanganese
intermediate 4. We conducted a preliminary experiment of cross-coupling
of two different Grignard reagents. Exposure of a mixture of p-methoxy-
phenylmagnesium bromide (1.0 equiv) and allylmagnesium chloride (2.0
equiv) in the presence of MnCl2 (20 mol %) with air provided p-
methoxyallylbenzene in 75% yield.
(11) Trost, B. M.; Tour, J. M. J. Am. Chem. Soc. 1988, 110, 5231.
Org. Lett., Vol. 5, No. 24, 2003
4625

tion. Finally, tetraallylmanganate induces cyclization of 1,2,6-
heptatriene.
Research Fellowships of the Japan Society for the Promotion
of Science for Young Scientists for financial support.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas (no. 412:
Exploitation of Multi-Element Cyclic Molecules) from the
Ministry of Education, Culture, Sports, Science, and Tech-
nology, Government of Japan. T.N. acknowledges the
Supporting Information Available: Experimental pro-
cedures and compound data. This material is available free
of charge via the Internet at http://pubs.acs.org.
OL035793J
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Org. Lett., Vol. 5, No. 24, 2003