Reaction of tert-Butyl Dibromoacetate or N,N-Diethyldibromoacetamide with Trialkylmanganate Providing an Alkylated Manganese Enolate

Full text of DOI:10.1021/jo971964k

910
J . Org. Chem. 1998, 63, 910-911
Sch em e 1
Rea ction of ter t-Bu tyl Dibr om oa ceta te or
N,N-Dieth yld ibr om oa ceta m id e w ith
Tr ia lk ylm a n ga n a te P r ovid in g a n Alk yla ted
Ma n ga n ese En ola te
Rie Inoue, Hiroshi Shinokubo, and Koichiro Oshima*
Department of Material Chemistry, Graduate School of
Engineering, Kyoto University, Sakyo-ku, Yoshida,
Kyoto 606-01, J apan
Sch em e 2
Received October 27, 1997
A multiple-component coupling reaction in one pot1 pro-
moted by various organometallics represents an extremely
powerful means to produce complex organic molecules. Our
interest in utilizing organomanganese reagents for selective
organic transformations prompted us to explore employment
of trialkylmanganate for a consecutive carbon-carbon bond
formation.
Ta ble 1. Rea ction of Dibr om o Am id e w ith
Tr ia lk ylm a n ga n a te
Recently, we have found that the treatment of gem-
dibromocyclopropanes with trialkylmanganate followed by
addition of an electrophile provided dialkylated cyclopro-
panes.2,3 The reaction proceeds as follows: (1) the initial
halogen-manganese exchange, (2) butyl migration under
Br- elimination, (3) second alkylation with an electrophile
such as iodomethane (Scheme 1). It then occurred to us that,
if both steps of the halogen-manganese exchange and alkyl
migration4 should proceed well, the reaction of dibromoac-
etate with tributylmanganate would provide an expeditious
route to butylated manganese enolate 4 (Scheme 2).5 We
have indeed found that treatment of tert-butyl dibromoac-
etate (1) with tributylmanganate followed by addition of an
electrophile such as benzaldehyde afforded a three-compo-
nent coupling aldol-type adduct 5a .
R23MnMtl
entry
amide 6
or R2MgX
electrophile
D2O
CH2dCHCH2Br 7b, 76
PhCHO
n-C6H13CHO
CH3I
yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
6a : R1 ) H
n-Bu3MnLi
n-Bu3MnLi
n-Bu3MnLi
n-Bu3MnLi
n-Bu3MnLi
7a , 82
6a
6a
6a
6a
6a
6a
6a
6a
6a
7c, 72a
7d , 77b
7e, 70
7f, 80
n-Bu3MnMgBr H2O
n-Bu3MnMgBr PhCHO
7c, 84c
7g, 95d
7h , 83
7i, 73e
7j, 89
Et3MnMgBr
Ph3MnMgBr
Ph3MnMgBr
PhCHO
H2O
PhCHO
H2O
CH2dCHCH2Br 7k , 51
PhCHO
A solution of tert-butyl dibromoacetate 16 (1.0 mmol) in
THF (3 mL) was added to tributylmanganate (1.4 mmol),7
generated from MnCl2 (1.5 mmol) and n-BuLi (4.4 mmol),
6b: R1 ) Me n-Bu3MnLi
6b
6b
n-Bu3MnLi
n-Bu3MnLi
7l, 90f
14
15
16
17
18
19
6a
6a
6a
6a
6a
6a
n-BuMgBr
n-BuMgBr
EtMgBr
EtMgBr
PhMgBr
PhMgBr
CH2dCHCH2Br 7b, 61
PhCHO
H2O
PhCHO
H2O
PhCHO
(1) Hall, N. Science 1994, 266, 32.
7c, 95g
7m , 74
7g, 80h
7h , 67
7i, 60i
(2) (a) Inoue, R.; Shinokubo, H.; Oshima, K. Tetrahedron Lett. 1996, 37,
5377. (b) Kakiya, H.; Inoue, R.; Shinokubo, H.; Oshima, K. Tetrahedron
Lett. 1997, 38, 3275.
(3) The reaction of gem-dibromocyclopropanes with dibutylcuprate and
tributylzincate has been reported. (a) Kitatani, K.; Hiyama, T.; Nozaki, H.
J . Am. Chem. Soc. 1976, 98, 2362. (b) Kitatani, K.; Hiyama, T.; Nozaki, H.
Bull. Chem. Soc. J pn. 1977, 50, 1600. (c) Harada, T.; Katsuhira, T.; Hattori,
K.; Oku, A. J . Org. Chem. 1993, 58, 2958. (d) Harada, T.; Hattori, K.;
Katsuhira, T.; Oku, A. Tetrahedron Lett. 1989, 30, 6035, 6039.
(4) Alkyl migration of R-haloborate: (a) Brown, H. C.; Rogic, M. M.;
Nambu, H.; Rathke, M. W. J . Am. Chem. Soc. 1969, 91, 2147. (b) Brown,
H. C.; Rogic, M. M.; Rathke, M. W.; Kabalka, G. W. J . Am. Chem. Soc. 1968,
90, 1911. (c) Brown, H. C.; Nambu, H.; Rogic, M. M. J . Am. Chem. Soc.
1969, 91, 6852. (d) Brown, H. C.; Nambu, H.; Rogic, M. M. J . Am. Chem.
Soc. 1969, 91, 6855. (e) Brown, H. C.; Rogic, M. M.; Rathke, M. W.; Kabalka,
G. W. J . Am. Chem. Soc. 1968, 90, 818.
(5) Very recently, generation of manganese enolates from R-acetoxycar-
bonyl compounds with tributylmanganate has been reported: Hojo, M.;
Harada, H.; Ito, H.; Hosomi, A. J . Am. Chem. Soc. 1997, 119, 5459. Other
methods for the generation of manganese enolates are as follows. Depro-
tonation: Cahiez, G.; Figadere, B.; Clery, P. Tetrahedron Lett. 1994, 35,
3065. Transmetalation: Cahiez, G.; Figadere, B.; Clery, P. Tetrahedron Lett.
1994, 35, 3069. 1,4-Addition: Cahiez, G.; Alami, M. Tetrahedron Lett. 1989,
30, 3541. Takai, K.; Ueda, T.; Kaihara, H.; Sunami, Y.; Moriwake, T. J .
Org. Chem. 1996, 61, 8728.
a
d
Syn/anti ) 65/35. b Syn/anti ) 69/31. c Syn/anti ) 49/51. Syn/
anti ) 49/51. e Syn/anti ) 49/51. f Isomeric ratio ) 36/61. Syn/
anti ) 45/55. Syn/anti ) 47/53. Syn/anti ) 51/49.
g
h
i
in THF (10 mL) at -78 °C. The mixture was warmed to 0
°C and stirred for 15 min at that temperature, and then
benzaldehyde (3.0 mmol) was added to the resulting mixture.
Extractive workup (AcOEt/water) followed by silica gel
column purification gave â-hydroxy ester 5a (syn/anti ) 77/
23)8 in 46% yield. An addition of iodomethane or 3-bro-
mopropene instead of benzaldehyde afforded the correspond-
ing adduct 5b or 5c in 42% or 69% yield, respectively.
The use of N,N-diethyldibromoacetamide (6a ) in place of
tert-butyl dibromoacetate (1) improved the yield of the
corresponding adducts.9 The representative results are
shown in Table 1 (entries 1-13). Several comments are
worth noting. (1) Manganate reagents, derived from MnCl2
(6) Treatment of ethyl dibromoacetate with tributylmanganate provided
acetoacetate derivative 14 in 32% yield along with an unidentified complex
mixture (see Scheme 6).
(7) (a) Cahiez, G. Butyl Manganese Chloride and Related Reagents. In
Encyclopedia of Reagents for Organic Synthesis; Paquette, L., Ed.; Wiley:
Chichester, 1995; p 925. (b) Cahiez, G. Manganese(II) Chloride. In Ency-
clopedia of Reagents for Organic Synthesis; Paquette, L., Ed.; Wiley:
Chichester, 1995; p 3227. (c) Cahiez, G. An. Quim. 1995, 91, 561. (d) Corey,
E. J .; Posner, G. H. Tetrahedron Lett. 1970, 315. (e) Okada, K.; Oshima,
K.; Utimoto, K. J . Am. Chem. Soc. 1996, 118, 6076. (f) X-ray of Ph6Mn2Li2:
Bartlett, R. A.; Olmstead, M. M.; Power, P. P.; Shoner, S. C. Organometallics
1988, 7, 1801.
(8) The isomeric ratio of 5a could not be improved when the aldol-type
reaction was conducted under kinetic conditions (at -78 °C, 5 min).
(9) The trapping experiment of an intermediary manganese enolate from
6a and n-Bu3MnLi by trimethylsilyl triflate resulted in the formation of
only N,N-diethylhexanamide. Thus, the isomeric ratio (E/Z) of the enolate
could not be determined.
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Communications
J . Org. Chem., Vol. 63, No. 4, 1998 911
Sch em e 3
Sch em e 4
Sch em e 5
and a Grignard reagent such as n-BuMgBr, EtMgBr, and
PhMgBr, proved to be equally as effective as lithium tri-
butylmanganate. This result is in sharp contrast to the
reaction of tert-butyl dibromoacetate (1) with tributylman-
ganate, generated from MnCl2 and butylmagnesium bro-
mide, which results in formation of a small amount of
butylated product 5 (E ) H) (<5% yield) along with a
complex mixture.10 (2) No products arising from attack of
the R-bromoenolate, BrCHdC(OMn-Bu2)NEt2 (8), on the
electrophile such as iodomethane or benzaldehyde could be
detected. This indicated that the migration of the alkyl
group on manganese to the adjacent carbon providing 3
occurred at a rate that was much faster than the rate of
conversion of BrCH(Mn-Bu2)CONEt2 (2) into the R-bromo
enolate 8. (3) Not only N,N-diethyldibromoacetamide (6a )
but also N,N-diethyldibromopropionamide (6b) reacted with
trialkylmanganate easily to give the expected adducts.
The reaction proceeded in the presence of a catalytic
amount of MnCl2. For instance, treatment of 6a (1.0 mmol)
with butylmagnesium bromide (3.0 mmol) in the presence
of MnCl2 (0.1 mmol) followed by an addition of 3-bromopro-
pene (3.0 mmol) provided 7b in 61% yield. The results are
also summarized in Table 1 (entries 14-19). Unfortunately,
the use of 6b (R1 ) Me) as a starting material in this
catalytic process resulted in a formation of diethyl-2-bro-
mopropionamide, and no butylated amide was observed.
The reaction was applied to a one-pot synthesis of R,â-
unsaturated amide.11 Treatment of 6a with (PhMe2-
Si)3MnLi, derived from PhMe2SiLi12 and MnCl2, followed by
addition of an aldehyde provided unsaturated amide 9 in
good yield as shown in Scheme 3.
Sch em e 6
Treatment of dibromo â-lactam 1013,14 with tributylman-
ganate gave butylated lactam 11a (trans/cis ) 26/74) in 62%
yield.15 An addition of 3-bromopropene or benzaldehyde
before quenching with water afforded 11b or 11c in 48%
(isomeric ratio ) 67/33) or 46% yield, respectively (Scheme
4).
The reaction of N,N-diethyldichloroacetamide (12) with
tributylmanganate (n-Bu3MnLi) provided N,N-diethyl-2-
chlorohexanamide (13a ) in 34% yield after the reaction
mixture was quenched with 1 M HCl. Thus, deprotonation
of the R-proton with tributylmanganate took place in prefer-
ence to the chlorine-manganese exchange in this case.
Treatment of 12 with lithium diisopropylamide followed by
tributylmanganate improved the yield of 13a up to 69%
yield. Quenching the reaction mixture with 3-bromopropene
or benzaldehyde gave allylated product 13b or a mixture of
13c and 13d (13c/13d ) 62/38) in 63% or 55% combined
yield (Scheme 5).
Su p p or tin g In for m a tion Ava ila ble: Experimental proce-
dures and compound characterization data (7 pages).
J O971964K
(10) Treatment of 1 with triethylmanganate or triphenylmanganate,
derived from MnCl2 and EtMgBr or PhMgBr, gave the corresponding
ethylated product or phenylated product in only 15% or 17% yield along
with an unidentified complex mixture, respectively, after quenching the
reaction mixture with water.
(11) From R-silyl amide: Woodbury, R. P.; Rathke, M. W. J . Org. Chem.
1977, 42, 1688. Woodbury, R. P.; Rathke, M. W. J . Org. Chem. 1978, 43,
1947. Peterson elimination reaction: Ager, D. J . Org. React. 1990, 38, 1.
(12) Gilman, H.; Lichtemwalter, G. D. J . Am. Chem. Soc. 1958, 80, 607.
(13) Manhas, M. S.; Khajavi, M. S.; Bari, S. S.; Bose, A. K. Tetrahedron
Lett. 1983, 24, 2323.
(14) Enolate of â-lactam: (a) DiNinno, F.; Beattie, T. R.; Christensen,
B. G. J . Org. Chem. 1977, 42, 2960. (b) Aimetti, J . A.; Kellogg, M. S.
Tetrahedron Lett. 1979, 3805. (c) Martel, A.; Daris, J .-P.; Bachand, C.;
Menard, M. Can. J . Chem. 1987, 65, 2179.
(15) Reduced lactam, 1,4-diphenyl-2-azetidinone, was also obtained in
27% yield as a byproduct.