Sequential 1,4-Addition and Ireland-Claisen Rearrangement Promoted by a Manganese-PbCl2-Me3SiCl System

Full text of DOI:10.1021/jo9618482

8728
J . Org. Chem. 1996, 61, 8728-8729
Sequ en tia l 1,4-Ad d ition a n d
Ir ela n d -Cla isen Rea r r a n gem en t P r om oted
by a Ma n ga n ese-P bCl2-Me3SiCl System 1
Kazuhiko Takai,* Takashi Ueda, Hiroya Kaihara,
Yoichi Sunami, and Toshio Moriwake
F igu r e 1. Potential electrophilic sites of allyl acrylate.
Ta ble 1. Effects of Ad d itives on 1,4-Ad d ition a n d
Sequ en tia l Rea r r a n gem en ta
Department of Applied Chemistry, Faculty of Engineering,
Okayama University, Tsushima, Okayama 700, J apan
Received September 30, 1996
Carbon-carbon bond formation from radicals provides
an attractive alternative to methods based on anions,
with carbon radicals having different selectivity from the
corresponding anionic reagents. As a result, this ap-
proach is being increasingly employed in organic syn-
thesis.2
Me3SiCl
(equiv)
additive
(equiv)
time
(h)
yield
yield
run
T (°C)
of 2b (%) of 3b (%)
1
2
3
4
5
0.1
1.0
3.0
3.0
3.0
90
25
25
25
25
3
47
48
43
14
7
0
43
31
81
92
0.5
0.5
0.5
0.5
Ketene silyl acetals of allylic esters are the precursors
of the Ireland-Claisen rearrangement3 and are usually
prepared by deprotonation and trapping with Me3SiCl.
A 1,4-addition to allylic acrylates and silylation can also
be used;4,5 however, since the acrylates have four poten-
tial electrophilic sites that can result in 1,2-addition (a),
1,4-addition (b), SN2 (c), and SN2′ (d) positions (Figure
1), it is necessary to control the regiochemistry. Alkyl-
lithium and magnesium reagents selectively add to the
carbonyl carbon in a 1,2-fashion, while dialkylcopper
lithium reagents react exclusively at the SN2′ position.4
Here, the 1,4-selectivity of alkyl radicals derived by
reduction with activated manganese6 was utilized in the
preparation of ketene silyl acetals. It was found that the
successive Ireland-Claisen rearrangement from the
intermediate silyl acetals proceeded smoothly at ambient
temperature.
DMAP, 3.0
NMI, 3.0
a
Reaction was conducted on a 1.0 mmol scale. Three mol of
isopropyl iodide, 6.0 mol of manganese, and 0.06 mol of PbCl2 were
used per mol of acrylate 1. R ) n-C5H11
b
.
Isolated yields.
product 3 were produced in 48% and 43% yields, respec-
tively, at 25 °C for 30 min (Table 1, run 2). This result
suggests that the rearrangement does not proceed from
a manganese enolate anion11 but, rather, occurs after
trapping to its silyl acetal. It is known that 4-(dimethy-
lamino)pyridine (DMAP) and N-methylimidazole (NMI)
accelerate the silylation step,12 and thus, when added,
the sequential Claisen rearrangement proceeded smoothly,
and the acid 3 was obtained in excellent yields (Table 1,
runs 4 and 5). The double bond produced was proven to
have E geometry as expected from the Ireland-Claisen
rearrangement.13
Primary, secondary, and tertiary alkyl iodides can be
used for the sequential 1,4-addition and Ireland-Claisen
rearrangement, the results of which are shown in Table
2.17 Because the reduction of a primary iodide proceeds
slower than that of a secondary iodide, in this case, the
reaction was conducted with 5 mol % of PbCl2 and heated
at 40 °C (Table 2, run 7). Although 1,4-addition occurred
smoothly with tert-butyl iodide in almost quantitative
yield, the successive rearrangement proceeded slowly,
Treatment of acrylate 1 with isopropyl iodide and
manganese7 activated by a catalytic amount of PbCl2
8
and Me3SiCl9 in a mixed solvent of DMF and THF at 90
°C for 3 h afforded 1,4-adduct 2 in 47% yield (Table 1,
run 1).10 When an equimolar amount of Me3SiCl was
used with the substrate, the adduct 2 and rearranged
(1) Dedicated to Clayton H. Heathcock on the occasion of his 60th
birthday.
(2) (a) Beckwith, A. L. J . Tetrahedron 1981, 37, 3073. (b) Stork, G.
Current Trends in Organic Synthesis; Nozaki, H., Ed.; Pergamon
Press: Oxford, 1983; p 359. (c) Ueno, Y. Synth. Org. Chem. J pn. 1984,
42, 1121. (d) Giese, B. Angew. Chem., Int. Ed. Engl. 1985, 24, 553. (e)
Curran, D. P. Synthesis 1988, 417, 489. Curran, D. P. In Comprehen-
sive Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon
Press: Oxford, 1991; Vol. 4, p 715.
(3) (a) Ireland, R. E.; Mueller, R. H. J . Am. Chem. Soc. 1972, 94,
5897. (b) Ireland, R. E.; Mueller, R. H.; Willard, A. K. J . Am. Chem.
Soc. 1976, 98, 2868. (c) Gajewski, J . J .; Emrani, J . J . Am. Chem. Soc.
1984, 106, 5733. (d) Ireland, R. E.; Wipf, P.; Armstrong, J . D., III. J .
Org. Chem. 1991, 56, 650. (e) Ireland, R. E.; Wipf, P.; Xiang, J .-N. J .
Org. Chem. 1991, 56, 3572. For reviews, see: Ziegler, F. E. Chem.
Rev. 1988, 88, 1423. Pereira, S.; Srebnik, M. Aldrichim. Acta 1993,
26, 17.
(4) Sequential 1,4-addition and Ireland-Claisen rearrangement was
accomplished with Grignard reagents under copper catalysis. Aoki,
Y.; Kuwajima, I. Tetrahedron Lett. 1990, 31, 7457.
(5) Hanamoto, T.; Baba, Y.; Inanaga, J . J . Org. Chem. 1993, 58, 299.
(6) Takai, K.; Ueda, T.; Ikeda, N.; Moriwake, T. J . Org. Chem. 1996,
61, 7990.
(7) Manganese powder was purchased from two sources: Rare
Metallic Co. (99% purity, -80 mesh) and Kojundo Chemical Laboratory
(99.9% purity, -50 mesh).
(8) PbCl2 (99.99% purity) was purchased from Rare Metallic Co.,
J apan.
(9) For activation of metals with Me3SiCl, see: J hingan, A. K.;
Maier, W. F. J . Org. Chem. 1987, 52, 1161. Knochel, P.; Yeh, M. C.
P.; Berk, S. C.; Talbert, J . J . Org. Chem. 1988, 53, 2390. Takai, K.;
Kakiuchi, T.; Utimoto, K. J . Org. Chem. 1994, 59, 2671. Fu¨rstner, A.;
Hupperts, A. J . Am. Chem. Soc. 1995, 117, 4468. Lautens, M.; Ren,
Y. J . Org. Chem. 1996, 61, 2210.
(10) Alkylmanganese compounds add to R,â-unsaturated carbonyl
compounds in a 1,4-fashion with the assistance of a catalytic amount
of CuCl. Cahiez, G.; Alami, M. Tetrahedron Lett. 1989, 30, 3541, 7365.
For reactions of alkylmanganese compounds, see: Cahiez, G.; Figadere,
B. Tetrahedron Lett. 1986, 27, 4445. Cahiez, G.; Laboue, B. Tetrahe-
dron Lett. 1989, 30, 7369. Kim, S.-H. K.; Hanson, M. V.; Rieke, R. D.
Tetrahedron Lett. 1996, 37, 2197.
(11) For Ireland-Claisen rearrangement via metal enolate of allylic
esters, see: (a) Zn: Baldwin, J . E.; Walker, J . A. J . Chem. Soc., Chem.
Commun. 1973, 117. (b) B: Corey, E. J .; Lee, D.-H. J . Am. Chem.
Soc. 1991, 113, 4026.
(12) Bassindale, A. R.; Stout, T. Tetrahedron Lett. 1985, 26, 3403.
(13) Authentic samples of γ,δ-unsaturated esters with E geometry
were prepared by the following route: (1) Inanaga’s Claisen rearrange-
ment;5 (2) esterification; (3) 1,4-addition. For comparison of the
geometry of the double bond, (Z)-methyl esters were prepared: (1)
dihydroxylation of (E)-methyl esters, OsO4, NMO/acetone, H2O, 25 °C,
5 h, 84-75%;14 (2) NaIO4, SiO2, CH2Cl2, 25 °C, 15 h, 69-55%;15
Ph3P(CH2)5CH3+Br-, NaN(SiMe3)2, -78 to +25 °C, 70-35%.16 In the
case of the Wittig olefination with benzylidenetripenylphosphorane (for
Table 2, run 3), a mixture of olefins (Z/E ) 26/74) was obtained.
(14) VanRheenen, V.; Kelly, R. C.; Cha, D. Y. Tetrahedron Lett. 1976,
1973.
(15) Daumas, M.; Vo-Quang, Y.; Vo-Quang, L.; Le Goffic, F. Syn-
thesis 1989, 64.
(16) Bestmann, H. J .; Stransky, W.; Vostrowsky, O. Chem. Ber.
1976, 109, 1694.
S0022-3263(96)01848-8 CCC: $12.00 © 1996 American Chemical Society

Communications
J . Org. Chem., Vol. 61, No. 25, 1996 8729
Ta ble 2. Sequ en tia l 1,4-Ad d ition a n d Ir ela n d -Cla isen
Rea r r ea n gem en ta
Sch em e 1
time yieldb
run R1
R2 R3
R4
R5 T (°C) (h)
(%)
E/Zc
1
2
3
4
5
6
7
8
i-Pr
H
H
H
H
Me
H
H
H
H
H
H
H
Me
H
n-C5H11
c-C6H11
Ph
-(CH2)5-
H
H
H
H
25
25
25
25
40
40
40
25
0.5
0.5
0.5
0.5
2
3
2
0.5
92
95
75
>99/<1
>99/<1
98/2
88
H
H
H
H
83d
75e
88f
H
n-Pr
t-Bu
n-C5H11
n-C5H11
>99/<1
H
H
52g >99/<1
a
Reaction was conducted on a 1.0 mmol scale. See typical
Treatment of propargylic acrylate 4 with isopropyl
iodide and the manganese system at 40 °C for 1 h
produced the corresponding allenic carboxylic acid 5 in
86% yield as a 1/1 mixture of diastereomers (eq 1).
procedure. Isolated yields. c Determined by 1H NMR and/or 13C
b
d
NMR analysis of the corresponding methyl ester. Anti/syn ) 48/
52. e 1,4-Adduct was obtained in 20% yield. f 5 mol % of PbCl2 was
g
used. 1,4-Adduct was produced in 42% yield. When the mixture
was treated at 40 °C for 3 h, the rearranged carboxylic acid was
produced in 53% yield along with the 1,4-adduct in 39% yield.
probably due to steric hindrance around the newly
formed carbon-carbon bond (Table 2, run 8). Heating
the mixture at 40 °C, however, did not improve the yield
of rearranged carboxylic acid. In contrast to the reported
Ireland-Claisen rearrangement,3b a substituent at R2 did
not accelerate the rearrangement. For example, the
reaction at 25 °C for 1 h produced the rearranged
carboxylic acid and 1,4-adduct in 30% and 47% yield,
respectively, while the reaction at 40 °C for 3 h produced
the acid in 83% yield (Table 2, run 5). The product in
run 5 was obtained as an anti/syn mixture of diastereo-
mers in a 48/52 ratio.3b The low diastereoselectivity
stems from the fact that both E and Z ketene silyl acetals
are produced in an almost 1/1 ratio under the condi-
tions.18
A plausible mechanism for this sequential reaction is
shown in Scheme 1. The reduction of an iodoalkane with
the manganese-PbCl2-Me3SiCl system produces the
corresponding alkyl radical 6, which has a sufficient
lifetime for intermolecular addition to an acrylate, even
under the reduction conditions. In contrast, reduction
of the adduct radical 7 takes place smoothly to give an
ester enolate that is trapped with Me3SiCl. The Ireland-
Claisen rearrangement and hydrolysis affords an (E)-γ,δ-
unsaturated acid. This sequential reaction is made
possible by the moderate manganese reducing system
discriminating between the two radicals 6 and 7.6
(17) Typ ica l P r oced u r e for 3. Me3SiCl (0.38 mL, 3.0 mmol) and
N-methylimidazole (NMI, 0.25 g, 3.0 mmol) were added at 25 °C to a
mixture of manganese powder (0.33 g, 6.0 mmol) and PbCl2 (17 mg,
0.060 mmol) in THF (4 mL) under an argon atmosphere, and the
mixture was stirred at 25 °C for 30 min. To the mixture was added a
solution of an allylic acrylate 1 (0.18 g, 1.0 mmol) in DMF (1 mL) at
25 °C. A solution of isopropyl iodide (0.51 g, 3.0 mmol) in DMF (1
mL) was then added to the mixture at 25 °C, producing an exothermic
reaction (ca. 35 °C). After the resulting mixture was stirred at 25 °C
for 30 min, saturated NH4Cl solution (10 mL) was added, and the
mixture was filtered with Celite and washed well with ether (3 × 10
mL). Organic extracts were washed with brine (10 mL), dried over
anhydrous MgSO4, and concentrated in vacuo. Purification of the
crude product by column chromatography on silica gel (hexane-ethyl
acetate, 30:1) gave the γ,δ-unsaturated acid 3 (0.21 g, 0.92 mmol) in
92% yield.
Ack n ow led gm en t. Financial support from the Ciba-
Geigy Foundation (J apan) for the Promotion of Science
and the Ministry of Education, Science and Culture of
J apan is gratefully acknowledged.
Su ppor tin g In for m ation Available: Characterization data
for all new compounds (4 pages).
J O9618482
(18) Trapping of the enolate derived from 2-phenylpropyl acrylate
and isopropyl iodide with manganese, PbCl2, and Me3SiCl produced E
and Z ketene silyl acetals in a 44/56 ratio.