A new type of allyl- And prop-2-ynyl-manganese species: Generation and reactions with electrophiles

Article abstract of DOI:10.1039/a705771g

Tetrabutylmanganese ate complex 'Bu₄MnLi₂' reacts with allylic and prop-2-ynylic bromides to generate the corresponding allyl- and prop-2-ynyl-manganese species which further react with electrophiles such as aldehydes, ketones, epoxide and chlorosilanes to afford the corresponding allylated and prop-2-ynylated and/or allenylated products in high yields.

Full text of DOI:10.1039/a705771g

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A new type of allyl- and prop-2-ynyl-manganese species: generation and
reactions with electrophiles
Makoto Hojo, Hajime Harada, Hajime Ito and Akira Hosomi*
Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305, Japan
Tetrabutylmanganese ate complex ‘Bu4MnLi2’ reacts with
allylic and prop-2-ynylic bromides to generate the corre-
sponding allyl- and prop-2-ynyl-manganese species which
further react with electrophiles such as aldehydes, ketones,
epoxide and chlorosilanes to afford the corresponding
allylated and prop-2-ynylated and/or allenylated products in
high yields.
action of the manganese ate complex as a reductant.2 Hitherto,
two methods for the generation of allylmanganese reagents, by
transmetalation3,4 and direct reduction of allyl halides with low
valent manganese (Grignard-type procedure),5 have been
reported.6‡ The present reaction is clearly different from these
reactions, in view of both the procedure and the reductant used.
The substantial difference between the reducing ability of
tributylmanganate and that of tetrabutylmanganate is also
interesting. Tributylmanganate seems possibly to be in equilib-
rium between dibutylmanganese and tetrabutylmanganate. Our
experiments showed that even reaction with tributylmanganate
gave allylated product, but the yield of the product did not
exceed 50% based on manganese. These results are likely due to
the disproportionation of tributylmanganate, and the present
reaction is the first example showing the peculiar reactivity of
tetraalkylmanganate, although comparable relative reactivities
of tetraalkylmanganates and trialkylmanganates have pre-
viously been reported.7§ Selected results for the allylation of
carbonyl compounds are summarized in Table 1.¶ Aliphatic and
aromatic aldehydes as well as ketones are allylated in high yield
under mild conditions.
A characteristic feature of the reactivity of the allylman-
ganese reagent also emerged, as shown in eqns. (2)–(4). From
chalcone 2e, the 1,4-adduct 3e was obtained as the major
product. This is in marked contrast to previously reported
reactions using low valent manganese, where only the 1,2-ad-
duct was produced.5,6∑ This selectivity may possibly be due to
the ate character of the allylmanganese reagent.8 The allylation
even took place with cyclohexene oxide,9** while with the keto
ester 2g, the keto moiety was allylated rather than the ester
function.6b
Reactions of many kinds of allyl- and prop-2-ynyl-metals have
been reported so far while new types of such reagents will
attract much attention.1 The creation of these new species may
provide new methods for selective allylation and prop-
2-ynylation. We report here reactions of a new type of allyl- and
prop-2-ynyl-manganese reagent generated by the direct reduc-
tion of allyl and prop-2-ynyl bromides using manganese ate
complex [eqn. (1)]. All of these reagents react with electrophiles
efficiently.
1) BunMnLin–2, THF
Br
(Mn)
reduction
conditions
1a
allylation
conditions
2) R1COR2
2
OH
(1)
R2
R1
Tributylmanganate ‘Bu3MnLi’ reacted with allyl bromide 1a
in THF at 278 °C, and upon addition of benzaldehyde 2a to the
mixture, the allylated product, 1-phenylbut-3-en-1-ol 3a was
obtained in 50% yield. Even if the amount of the manganate was
increased to 1.5 equiv. the yield of the product 3a was at most
66% [eqn. (1), R1 = Ph, R2 = H]. In sharp contrast to these
facts, tetrabutylmanganate ‘Bu4MnLi2’ showed high reactivity
and the allylated product 3a was produced in 80% yield using an
equimolar amount of the reagent.† These results deserve
comment. Considering this stepwise procedure, an allylmanga-
nese reagent is possibly generated from allyl bromide by the
Tetrabutylmanganate also reduced prop-2-ynylic bromides
[eqn. (5)]. In this case, allenic and/or prop-2-ynylic products
were produced depending on the bulkiness of the electrophiles
and the substituent R on the prop-2-ynyl bromides (Table 2).
From prop-2-ynyl bromide 1d (R = H), only the prop-2-ynylic
adduct 3o was obtained in quantitative yield [eqn. (6)].††
As shown here, tetrabutylmanganate reacts with allyl and
prop-2-ynyl bromides to generate allyl- and prop-2-ynyl-
Table 1 Generation of an allylmanganese reagent from allyl bromide 1a via reduction with manganese ate complexes and its reaction with carbonyl
compounds 2a
Carbonyl compound 2
Manganese ate
complex (equiv.)
Reduction
conditions
Allylation
conditions
R1
R2
Product
Yield (%)b
‘Bu3MnLi’ (1.0)
‘Bu3MnLi’ (1.5)
‘Bu4MnLi2’ (1.0)
‘Bu4MnLi2’ (1.0)
‘Bu4MnLi2’ (1.0)
‘Bu4MnLi2’ (1.0)
278 °C, 1 h
278 °C, 1 h
298 °C, 1 h
298 °C, 1 h
298 °C, 1 h
298 °C, 1 h
Ph
Ph
Ph
Pr
H
H
H
H
2a
2a
2a
2b
2c
2d
278 °C to room temp., 4 h
278 °C to room temp., 4 h
278 °C, 0.5 h
3a
3a
3a
3b
3c
3d
50
66
80
70
76
84
278 °C, 3 h
Ph
-(CH2)5-
Me
298 °C to room temp., 4 h
278 °C, 3 h
a Conditions: allyl bromide 1a (0.50 mmol) was added to a mixture of manganese ate complex (0.50 mmol) in THF at the temperature shown in the column
‘reduction conditions’, and the mixture stirred for 1 h. An electrophile was added to the flask, and the resultant mixture was further stirred under the conditions
shown in the column ‘allylation conditions’. After quenching with saturated NH4Cl and extraction with Et2O (30 ml 3 3), an organic layer was washed with
saturated EDTA and saturated NaHCO3, and the organic layer was dried over MgSO4. After evaporation of solvents, the crude mixture was subjected to
chromatography to give the pure product. b Isolated yield.
Chem. Commun., 1997
2077

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1) Bu4MnLi2, THF
–78 °C, 1 h
O
Br
E
E
•
+
(5)
Ph
Ph
2) Electrophile (E+),
–78 °C to room temp.
R
R
3e 46%
1) Bu4MnLi2, THF, –98 °C, 1 h
O
R
1a
+
1b R = C6H13
3h–n
c R = Ph(CH2)3
OH
2)
4
–78 °C, 3 h
Ph
Ph
(2)
(3)
(4)
2e
Ph
Ph
3e′ 33%
Ph
1) Bu4MnLi2, THF, –78 °C, 1 h
Br
(6)
1) Bu4MnLi2, THF, –98 °C, 1 h
2) 4 PhCHO, –78 °C to room temp., 12 h
OH
1a
1a
1d
3o 99%
O
HO
2) 3
–78 °C to room temp., 12 h
2 f
3f 60%
Footnotes and References
* E-mail: hosomi@staff.chem.tsukuba.ac.jp
1) Bu4MnLi2 / THF, –98 °C, 1 h
O
O
O
† The formulae ‘Bu3MnLi’ and ‘Bu4MnLi2’ and the terms ‘tributyl-
manganate’ and ‘tetrabutylmanganate’ are used tentatively, since the
precise structures of the species are not clear at present.
‡ Barbier-type allylations with metallic manganese were also reported (ref.
6).
–78 °C, 3 h
2) 4
3g 42%
CO2Me
2g
§ It is known that the reactions of tetraalkylmanganates with acyl chlorides
to produce ketones proceed at lower temperature, compared to the reactions
of trialkylmanganates, while the yields in these reactions are equally good
[ref. 7(a)].
Table 2 Generation and reaction of allenyl- and prop-2-ynyl-manganese
speciesa
¶ A solution of BuLi in hexane (1.6 m; 1.25 ml, 2.0 mmol) was added at
220 °C to a suspension of manganese(ii) chloride in THF (63 mg, 0.50
mmol in 5 ml) and the mixture was stirred at 240 to 220 °C for 30 min.
Allyl or prop-2-ynyl bromide (0.50 mmol) was added at 298 or 278 °C (at
the specified temperature), and the mixture was stirred for 1 h. An
electrophile (1.5–2.5 mmol) was added to the mixture, which was further
stirred under the conditions shown. After quenching with saturated NH4Cl
and extraction with Et2O (30 ml 3 3), the organic layer was washed with
saturated ethylenediaminetetraacetic acid (EDTA) and saturated NaHCO3.
The organic layer was dried over MgSO4. After evaporation of solvents, the
crude mixture was subjected to chromatography to give the pure product.
∑ The selective 1,4-addition to ethylidenemalonate, which is a good acceptor
for the 1,4-addition [cf. refs. 3(c), 5, 6 and 8], using allylmanganese chloride
was also reported [ref. 3(c)].
Prop-2-ynyl
bromide
Yield (%)b
(allenic:prop-2-ynylic)
Electrophile
Product
1b
1b
1b
1b
1c
1c
1c
PhCHO 2a
EtCHO 2h
PhCOMe 2c
Et2CO 2i
PhMe2SiCl 2j
Me3SiCl 2k
Me2HSiCl 2l
3h
3i
3j
3k
3l
3m
3n
82 (100:0)
75 (100:0)
74 (100:0)
82 (67:33)
80 (0:100)
94 (1:99)
86 (61:39)
a Conditions: prop-2-ynyl bromide (0.50 mmol) was added to a mixture of
‘Bu4MnLi2’ (0.50 mmol) in THF at 278 °C, and the mixture was stirred for
1 h. An electrophile was added to the flask, at 278 °C and the temperature
was allowed to rise to room temp. over > 4 h. After quenching was saturated
NH4Cl and extraction with Et2O (30 ml 3 3), the organic layer was washed
with saturated EDTA and saturated NaHCO3, and the organic layer was
dried over MgSO4. After evaporation of solvents, the crude mixture was
subjected to chromatography to give the pure product. b Isolated yield.
** It was reported that alkylmanganese chloride reacted with oxiranes in the
presence of a copper chloride catalyst (ref. 9).
†† This is to the best of our knowledge, the first case of the generation and
reaction of prop-2-ynylic manganese reagents.
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4 K. Okada, K. Oshima and K. Utimoto, J. Am. Chem. Soc., 1996, 118,
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manganese reagents where the manganate serves as a reducing
agent, not as an alkylating agent. This is a new approach to
allylic and prop-2-ynylic manganese reagents which react with
aldehydes, ketones, oxirane and chlorosilanes to give the
corresponding allylated and prop-2-ynylic and/or allenic prod-
ucts. Further study on the generation and reaction of these
reagents is now under investigation.
This work was partly supported by Grants-in-Aid for
Scientific Research and Grants-in-Aid for Scientific Research
on Priority Areas from the Ministry of Education, Science,
Sports and Culture, Japan and Pfizer Pharmaceuticals Inc. H. H.
acknowledges support from the Research Fellowships of the
Japan Society for the Promotion of Science for Young
Scientists.
5 T. Hiyama, M. Obayashi and A. Nakamura, Organometallics, 1982, 1,
1249.
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(b) G. Cahiez and P.-Y. Chavant, Tetrahedron Lett., 1989, 30, 7373.
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G. Cahiez, P.-Y. Chavant and E. Metais, Tetrahedron Lett., 1992, 33,
5245.
8 G. Cahiez and M. Alami, Tetrahedron Lett., 1986, 27, 569.
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Received in Cambridge, UK, 7th August 1997; 7/05771G
2078
Chem. Commun., 1997